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Can Personalized Diets Help Control Blood Sugar?

April 30, 2024 by Dr. Steve Chaney

What Does This Study Mean For You?

Author: Dr. Stephen Chaney

Personalized diets are highly advertised. We are told to forget the old “one size fits all” diets of the past. We are told we are all different, so diets should be individualized to us.

We are promised that by collecting DNA samples from our tissue or bacteria in our gut, blood samples, and personal medical history, a personalized diet can be created that “fits us like a glove”.

But are those promises true, or are they hype? Diets to control blood sugar spikes should be a perfect topic for testing those claims. Millions of Americans have trouble controlling their blood sugar levels. Specifically:

1 million adults (14.7% of US adults) have diabetes, mostly type 2 diabetes.

6 million adults (38.0% of US adults) have prediabetes.

- That amounts to 52% of the US population who have trouble controlling blood sugar levels.

Previous studies have shown that prediabetes and type 2 diabetes are largely reversible with diet and lifestyle change.

Recent studies have shown tremendous inter-person variability in the blood sugar response to any given food.

Previous studies have shown that our gut bacteria influence our blood sugar response to foods.

In theory, blood sugar control should be the perfect candidate for personalized diets. With that in mind, the authors of this study have created an algorithm called PNP (Personal Nutrition Program) that combines continuous blood glucose monitoring, HbA1c measurement (a measure of blood sugar control), personal characteristics (physical activities, sleep times, stress, and hunger), and a DNA analysis of stool samples to identify the species of gut bacteria. They also created a PNP app to allow participants to monitor and modify the foods they ate on a continuous basis.

In this study (AY Kharmats et al, The American Journal of Clinical Nutrition, 118: 443-451, 2023) the authors compared the effectiveness of their Personalized Nutrition Program algorithm with a standard, one-size-fits-all, low fat diet for improving blood sugar control in patients with prediabetes and type 2 diabetes.

Note: They used a low fat diet because, despite what you may have heard, low fat diets are better than low carb diets for diabetics. Of course, the low fat diet they used was created by dietitians. The carbohydrates came from whole foods rather than added sugars.

How Was The Study Done?

The investigators recruited 156 participants from the NYU Langone Health Center between January 2018 and March 2021. The participants selected were overweight with prediabetes or moderately controlled type 2 diabetes. For participants with type 2 diabetes, it was managed with lifestyle alone or lifestyle plus metformin. Other characteristic of the study participants were:

Gender: 33.5% male, 66.5% female.
Race & Ethnicity: 55.7% white, 24.1% black, 16.5% Hispanic.
Education: 69.5% with a college degree.
Baseline BMI: 33 (Obese).
Baseline HbA1c: 5.8% (prediabetic range) with 12% of participants ≥6.5% (diabetic range).

The participants were randomly divided into two groups that were matched with respect to weight and blood sugar control. One group was put on a diet based on the investigator’s PNP algorithm. The other group was put on a standardized low fat (< 25% of calories from fat) diet that is often used with diabetic patients.

Upon admission to the study, blood samples were drawn for HbA1c, a detailed questionnaire was filled out, and stool samples were obtained for DNA analysis to identify the species of bacteria in their gut.

Each participant was given a continuous glucose monitoring device to wear during the study. This allowed the investigators to monitor the participants blood sugar control throughout the study.

All this information was used to provide individual diet recommendations for the personalized diet group using the PNP algorithm developed by the investigators.

The study lasted 6 months and measured improvements in blood sugar control as assessed by a decrease in blood sugar spikes and a reduction in HbA1c.

Both Groups were put on a registered dietitian-led behavioral intervention program targeting 7% weight loss and a calorie deficit goal of 500 calories per day. The 1-hour sessions were conducted by Webex weekly for 4 weeks and then every other week for the remaining 5 months. The sessions included:

Education (e.g., obesity risks, benefits of weight loss, strategies for restricting calories, protocols for aerobic exercise and strength training, and dealing with weight loss plateaus)

Behavioral change (e.g., importance of behavioral change, goal setting, self-reward, and problem-solving around common barriers to weight loss success)

The participants were advised to gradually build up to 150 min/week of moderate intensity exercise.

Each participant was given access to the PNP mobile app designed by the investigators. The app provided real-time feedback regarding their dietary intake relative to the target specific to their group (low fat diet or personalized diet). Participants were asked to use the app to:

Enter their dietary intake and self-monitor their meals (If the meal did not match the target specific to their group, the participants were trained how to substitute other foods, so their meal better matched their target.)

For the Standardized Low Fat Group, the PNP app provided real-time feedback regarding calorie intake and macronutrient distribution for meals and snacks logged in by the participants.

For the Personalized Group the PNP app scored meals as excellent, very good, good, bad, or very bad based on the PNP algorithm developed by the investigators.

Can Personalized Diets Help Control Blood Sugar?

The results were clear-cut:

Weight loss was identical on both diets. This is no surprise. The study design included an exceptionally well-designed weight loss protocol for both groups.

The decrease in HbA1c was identical on both diets.

The improvement in blood sugar control was identical on both diets.

The investigators concluded, “[The] personalized diet did not result in an increased reduction in GV [blood sugar control] or HbA1c in patients with prediabetes or moderately controlled type 2 diabetes compared to a standardized diet.”

Since the investigators had designed the algorithm used to create personalized diets for this study, this was probably not the result they wanted.

So, they added, “Additional subgroup analyses may help to identify patients who are more likely to benefit from this personalized intervention.”

What Does This Study Mean For You?

This first takeaway from this study was obvious:

The personally designed diet did not perform any better than a standard, one size fits all, diet at improving blood sugar control.

Of course, this was not any standard diet. It was a diet that has been used successfully with diabetics for years. However, a lot of research had gone into developing the personalized diet. One might have expected it to perform better.

This is not the first study in which a personalized diet has performed no better than a standard diet. It doesn’t mean that the concept behind personalized diets is faulty. It just means we don’t yet know enough to design a personalized diet that really works.

The second takeaway from this study might be less obvious:

Weight loss is the most important factor for improving blood sugar control. Any diet that reduces weight will improve blood sugar control. This is also true for many other health issues such as high cholesterol, high blood pressure, high triglycerides, and osteoarthritis.

However, this should not come as a surprise either.

- Vegan and keto diets are polar opposites. Yet both give similar short-term weight loss and provide similar short-term health benefits.

- Studies have shown that intermittent fasting gives no better weight loss and health benefits than any diet that cuts calories to a similar extent.

- In other words, the diet you choose or the way you choose to restrict calories doesn’t matter. It is weight loss that provides the health benefits.

However, diet does appear to matter in the long term. If you look at studies ranging from 10 to 30 years, primarily plant-based diets provide better health benefits than primarily meat-based diets. And diets consisting primarily of whole, unprocessed foods provide better health benefits than diets high in processed foods.

Finally, there is an important corollary to this study showing that a personalized diet performed no better than a standardized diet at controlling blood sugar.

Some companies are trying to sell you expensive personalized diets with extravagant claims about the health benefits of their diet. Be wary of those diets. The science supporting their diets is premature. Their claims may be misleading.

And if the companies claim their diet is supported by published clinical studies, you should evaluate those studies carefully. The study I reviewed in this article was an exceptionally well-designed study. Any study that does not control for weight loss is likely to provide misleading results.

The Bottom Line

A recent study compared the effectiveness of a personalized diet and a standardized diet in improving blood sugar control for patients with prediabetes or type 2 diabetes. The results were clear-cut:

Weight loss was identical on both diets. This is no surprise. The study design included an exceptionally well-designed weight loss protocol for both groups.

The decrease in HbA1c was identical on both diets.

The improvement in blood sugar control was identical on both diets.

This doesn’t mean that the concept behind personalized diets is faulty. It just means we don’t yet know enough to design a personalized diet that really works.

For more information on this study and what it means for you, read the article above.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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My posts and “Health Tips From the Professor” articles carefully avoid claims about any brand of supplement or manufacturer of supplements. However, I am often asked by representatives of supplement companies if they can share them with their customers.

My answer is, “Yes, as long as you share only the article without any additions or alterations. In particular, you should avoid adding any mention of your company or your company’s products. If you were to do that, you could be making what the FTC and FDA consider a “misleading health claim” that could result in legal action against you and the company you represent.

For more detail about FTC regulations for health claims, see this link.

https://www.ftc.gov/business-guidance/resources/health-products-compliance-guidance

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About The Author

Dr. Chaney has a BS in Chemistry from Duke University and a PhD in Biochemistry from UCLA. He is Professor Emeritus from the University of North Carolina where he taught biochemistry and nutrition to medical and dental students for 40 years. Dr. Chaney won numerous teaching awards at UNC, including the Academy of Educators “Excellence in Teaching Lifetime Achievement Award”.

Dr Chaney also ran an active cancer research program at UNC and published over 100 scientific articles and reviews in peer-reviewed scientific journals. In addition, he authored two chapters on nutrition in one of the leading biochemistry text books for medical students.

Since retiring from the University of North Carolina, he has been writing a weekly health blog called “Health Tips From the Professor”. He has also written two best-selling books, “Slaying the Food Myths” and “Slaying the Supplement Myths”. And most recently he has created an online lifestyle change course, “Create Your Personal Health Zone”. For more information visit https://chaneyhealth.com.

For the past 45 years Dr. Chaney and his wife Suzanne have been helping people improve their health holistically through a combination of good diet, exercise, weight control and appropriate supplementation.

What Role Should DNA Testing Play In Nutritional Recommendations?

May 2, 2023 by Dr. Steve Chaney

The Promise And Problems Of Nutrigenomics

Author: Dr. Stephen Chaney

When the human genome was sequenced in 2003, many of us in the scientific community thought we were on the verge of a revolution in human health and longevity. We would soon be able to tell individuals their risk of developing various diseases.

Even better, we would be able to tell them the kind of diet and supplementation they needed to avoid those diseases. We would be able to personalize our nutritional recommendation for every individual based on their genome – something called nutrigenomics.

How naive we were! It has turned out to be much more complicated to design personalized nutrition recommendations based on someone’s genome than we ever imagined.

What Is Nutrigenomics?

As a Professor at the University of North Carolina I specialized in cancer drug development for over 30 years. Over the last decade of my career a ﬁeld called pharmacogenomics became widely accepted in the ﬁeld of cancer drug development. In simple terms, pharmacogenomics looks at how an individual’s genes influence the effectiveness and side effects of drugs.

Because of pharmacogenomics, drugs today are being approved to target cancers for people whose cancer cells have a particular genetic makeup. These drugs would not have been approved a decades ago because if you test them on cancer in the general population, they have little or no eﬀectiveness. They only work on a subset of people who have a form of cancer with a specific genetic makeup.

In principle, nutrigenomics is the same principle. You’ve heard for years that we all have unique nutritional needs. Now we are starting to learn why. It’s because we all have unique variations in our genetic makeup. These genetic mutations increase our risk of certain diseases, and they increase our needs for certain nutrients.

For example, mutations in the MTHFR gene increase the risk of certain birth defects, and supplementation with folic acid is particularly important for reducing birth defects in that population group.

Similarly, mutations in the vitamin D receptor, the VDR gene, interfere with vitamin D absorption from foods and are associated with a condition known as “vitamin D-resistant rickets”. Babies born with this genetic defect require mega doses of vitamin D for normal bone formation.

These are the best-established examples of gene mutations that affect nutritional needs. Many more gene-nutrient interactions have been proposed, but they have not been validated by follow-up experiments.

The situation is similar when we look at gene mutations associated with metabolic responses such as fat and carbohydrate metabolism, obesity, insulin resistance and type 2 diabetes. There are a few gene mutations that have strong associations with obesity and diabetes. Many more gene-metabolism interactions have been proposed, but the data are weak and inconsistent.

The Promise And Problems Of Nutrigenomics

The Promise Of Nutrigenomics.

Now that you understand what nutrigenomics is and have some background information about it, let’s look at the promise of nutrigenomics. One promise of nutrigenomics is personalized supplement programs.

We all have different nutritional needs. Wouldn’t it be wonderful if someone could analyze your genome and provide you with a personalized supplement program that precisely fits your genetically determined nutritional requirements?

There are companies that offer such personalized supplement programs. Are they providing you with something of value or is their testing bogus? Are their supplements worthless?

Another promise of nutrigenomics is personalized diet advice. Some people seem to do better on low-fat diets. Other people do better on low-carb diets. Saturated fats and red meats may be more problematic for some individuals than for others. Wouldn’t it be wonderful if someone could analyze your genome and provide you with a personalized diet program – one that allows you to lose weight easily and gain vibrant health.

There are companies that will analyze your genome and tell you whether you are more likely to lose weight and be healthier on a low-fat or low-carbohydrate diet. Is their testing accurate or is it bogus? Are they providing you with useful information, or is their diet advice worthless?

The Problem With Nutrigenomics

The short answer to the questions I posed in the previous section is that personalized supplement and diet programs are on the horizon, but we are not there yet. Companies promising you personalized nutrition programs based only on DNA tests are misleading you. They quote a few studies supporting the tests they run and ignore the many studies showing their tests are worthless.

In case you think that is just my opinion, let me quote from some recent reviews on the current status of nutrigenomics.

For example, a review (C Murgia and MM Adamski, Nutrients, 366, 2017) published in 2017 concluded: “The potential applications to nutrition of this invaluable tool were apparent since the genome was mapped. The first articles discussing nutrigenomics and nutrigenetics were published less than a year after the first draft of the human DNA sequence was made available…However, fifteen years and hundreds of publications later, the gap between the experimental and epidemiologic evidence and health practice is not yet closed.”

“The [complexity] of the genotype information is not the only factor that complicates this translation into practice. The discovery of other levels of control, including epigenetics [modifications of DNA that affect gene expression] and the intestinal microbiome, are other complicating factors. While the science of nutritional genomics continues to demonstrate potential individual responses to nutrition, the complex nature of gene, nutrition and health interactions continues to provide a challenge for healthcare professionals to analyze, interpret and apply to patient recommendations.”

Another review (M Gaussch-Ferre et al, Advances in Nutrition, 9: 128-135, 2018) published in 2018 concluded: “Overall, the scientific evidence supporting the dissemination of genomic information for nutrigenomic purposes remains sparse. Therefore, additional knowledge needs to be generated…”

In short, the experts are saying we still don’t know enough to predict the best diets, or the best supplements based on genetic information alone. Why is that? Why is it so complicated? In part, it can be explained by a term called penetrance. Penetrance simply means that the same gene mutation can have different effects in different people. In some people, its effects may be barely noticeable. In other people its effects may be debilitating.

The Truth About DNA Testing And Personalized Nutrition

Penetrance is just a word. It’s a concept. The important question is, “What causes differences in genetic penetrance?” Here are the most likely explanations.

1) Human genetics is very complex. There are some gene mutations, such as those causing cystic fibrosis and sickle cell anemia, that can cause a disease by themselves. Most gene mutations, however, simply predispose to a disease or metabolic disturbance and are highly influenced by the activity of other genes. That’s because the products of gene expression form intricate regulatory and metabolic networks. When a single gene is mutated, it interacts with many other genes in the network. And, that network is different for each of us.

2) Many common diseases are polygenic. That includes diseases like heart disease, diabetes, and most cancers. Simply put, that means that they are not caused by a single gene mutation. They are caused by the cumulative effect of many mutations, each of which has a small effect on disease risk. The same appears to be true for mutations that influence carbohydrate and fat metabolism and affect nutrient requirements.

3) The outcome of gene mutations is strongly influenced by our diet, lifestyle, and environment. For example, a common mutation in a gene called FTO predisposes to obesity. However, the effect of this mutation on obesity is strongest when it is coupled with inactivity and foods of high caloric density (translation: junk foods and fast foods instead of fresh fruits and vegetables). Simply put, that means most of us are genetically predisposed to obesity if we follow the American lifestyle, but obesity is not inevitable.

4) Epigenetics has an important influence on gene expression. When I was a graduate student, we believed our genetic destiny was solely determined by our DNA sequence. That was still the prevailing viewpoint when the human genome project was initiated. We thought that once we had our complete DNA sequence, we would know everything we needed to know about our genetic destiny.

How short sighted we were! It turns out that our DNA can be modified in multiple ways. These modifications do not change the DNA sequence, but they can have major effects on gene expression. They can turn genes on or turn them off. More importantly, we have come to learn that these DNA modifications can be influenced by our diet, lifestyle, and exposure to environmental pollutants.

This is the science we call epigenetics. We have gone from believing we have a genome (DNA sequence) that is invariant and controls our genetic destiny to understanding that we also have an “epigenome” (modifications to our DNA) that is strongly influenced by our diet, lifestyle, and environment and can change day-to-day.

5) Our microbiome has an important influence on our health and nutritional status. Simply put, the term microbiome refers to our intestinal microbes. Our intestinal bacteria are incredibly diverse. Each of us has about 1,000 distinct species of bacteria in our intestines.

Current evidence suggests these intestinal bacteria influence our immune system, inflammation and auto-immune diseases, brain function and mood, and our predisposition to weight gain – and this may just be the tip of the iceberg.

More importantly, our microbiome is influenced by our diet. For example, vegetarians and meat eaters have entirely different microbiomes. Furthermore, the effect of diet on our microbiome is transitory. If you change your diet, the species of bacteria in your microbiome will completely change in a few weeks.

Finally, our microbiome also influences our nutritional requirements. For example, some species of intestinal bacteria are the major source of biotin and vitamin K2 for all of us and the major source of vitamin B12 for vegans. Intestinal bacteria may also contribute to our supply of folic acid and thiamine. Other intestinal bacteria inactivate and/or remove some vitamins from the intestine for their own use. Thus, the species of bacteria that populate our intestines can influence our nutritional requirements.

Now that you know the complexity of gene interactions you understand why we are not ready to rely on DNA tests yet. We don’t yet know enough to design a simple DNA test to predict our unique nutritional needs. That science is at least 10-20 years in the future. Companies that tell you otherwise are lying to you.

What Role Should DNA Testing Play In Nutritional Recommendations?

The algorithms that are most successful in creating personalized diet and/or supplement recommendations:

1) Start with an analysis of your diet and lifestyle. They powerfully affect both gene expression and your microbiome.

2) Add in health parameters such as blood pressure, LDL cholesterol, HDL cholesterol, triglycerides, and hemoglobin A1c (a measure of blood sugar control). For example, a DNA analysis may suggest you are at risk for having elevated cholesterol, but whether you do or not is influenced by many other factors. A simple blood test indicates whether that risk is real for you.

3) Consider your personal health goals. If nutritional recommendations are to be personalized to you, they should emphasize the health goals you value most.

4) Include any diseases you have and recommendations of your doctor. If your doctor has recommended you lower your blood pressure, your cholesterol, or blood sugar levels, that is valuable information to include in the mix.

5) Now you are ready to include DNA testing in the mix. It can provide some valuable insights, but those insights need to be filtered through the lens of all the critical information collected in the first four steps. Genetics gives you possibilities. The information collected in the first four steps represents your realities.

The Bottom Line

Nutrigenomics is defined as the interaction between our genetic makeup and our diet. How far have we advanced in the science of nutrigenomics? Can a simple DNA test provide us with useful information?

For example, we all have different nutritional needs. Wouldn’t it be wonderful if someone could analyze your genome and provide you with a personalized supplement program that precisely fits your genetically determined nutritional requirements?

There are companies that will analyze your genome and offer personalized supplement programs. Are they providing you with something of value or is their testing bogus? Are their supplements worthless?

Two recent reviews have surveyed the nutrigenomic literature (all published clinical studies) and have concluded that we still don’t know enough to predict the best diets, or the best supplements based on genetic information alone. Why is that? It is because:

1) Human genetics is very complex.

2) Many common diseases are polygenic (caused by the cumulative effect of many mutations).

3) The effect of gene mutations on our health and wellbeing is strongly influenced by our diet, lifestyle, and environment.

4) Epigenetics has an important influence on gene expression.

5) Our microbiome has an important influence on our health and nutritional status.

For more details on these studies and the kind of testing that best determines the right diet and/or supplement program for you, read the article above.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

Personalized Nutrition Tests Help Gain Control Of Your Blood Sugar

July 30, 2019 by Dr. Steve Chaney

What Is The Truth About Personalized Nutrition Testing? – Part 1

Author: Dr. Stephen Chaney

Personalized nutrition testing is all the rage. Should you limit carbs or should you limit fats? Should you avoid sugar? Should you eat more protein or less protein? What supplements should you take?

Companies promise you that their version of personalized nutrition testing will tell you all that and more. Are they being truthful or are their claims false? Are the personalized nutrition tests they offer valuable or are they a waste of money?

In particular, recent headlines have proclaimed that a new personalized testing system can help you do a better job of controlling your blood sugar levels. Is this claim true?

Let me answer that question in 3 steps:

First, I will discuss why that kind of test could be valuable and describe how the study was done.
Next, I will evaluate the strengths and weaknesses of the study.
Finally, I will discuss why personalized nutrition testing is so difficult. I will also give you guidance on how you can gain better control of your blood sugar fluctuations without expensive tests.

Why Is Predicting How To Control Blood Sugar Important?

Why is it important to devise a personalized nutrition test to measure an individual’s blood sugar response to various foods? The answers to this are twofold:

The combination of the obesity epidemic and the American diet have created the perfect storm. Millions of Americans have high blood sugar levels. Elevated blood sugar levels are associated with heart disease, diabetes, cancer, inflammatory diseases and much more. This is a public health crisis.
Keeping track of carbohydrates in the foods you eat is not a particularly effective way to control your blood sugar levels. This approach is based on average responses, and none of us are average. I have discussed individual variation in blood sugar responses to common foods in a previous issue of “Health Tips From The Professor.”

How Was The Study Done?

The study (H Mendes-Soares et al, American Journal of Clinical Nutrition, 110: 63-75, 2019) enrolled 327 participants, primarily from two counties in Minnesota. The characteristics of the participants was as follows:

77% female.
Average age 45.
64% overweight and 27% obese which, unfortunately, is average for the American population.
HbA1c (a measure of long-term blood glucose control) averaged 5.2, with 8.4% of the population having elevated HbA1c (indicative of chronic high blood sugar levels and consistent with pre-diabetes).

The study lasted one week and was rigorously controlled.

The subjects provided a stool sample 2 days prior to the study. The stool sample was used to characterize the populations of gut bacteria (microbiome) for every subject.
Prior to the study, the subjects were also asked to fill out a questionnaire asking about their health, lifestyle, activities, and diet preferences. Height, weight, blood pressure, and HbA1c levels were also measured.
Subjects were given phone apps to record their food (meal content, duration, and time) and activity (intensity, duration, and time) throughout the week. They were also asked to record medications and sleep.
Subjects were outfitted with a glucose monitor that measured blood glucose levels continuously throughout the week. The subjects were also instructed to use a manual blood glucose monitor 4 times a day. This served as a check on the accuracy of the continuous blood glucose monitor.
On 4 days the subjects were given a standardized breakfast consisting of a bagel with cream cheese. This allowed estimation of variation in blood sugar response between subjects and day to day variations in blood sugar response for individual subjects.
Finally, the subjects were told to maintain their normal eating habits with no significant deviations during the week.

All this information was used to develop a personalized model to predict the blood sugar response of each subject to various foods. However, this was no ordinary model. It was not just using the subject’s genome or microbiome to predict their blood sugar response to foods. The model included:

Microbiome: Population of gut bacteria. This information came from the stool test.
Meal information: carbohydrate, fat, protein, sugar, fiber, calories, sodium, alcohol, & water. This information came from the food app on their phones that the subjects used to log everything they ate for a week.
Meal context: Time of day, total carbohydrate consumed over past 3 hours and 6 hours, total calories consumed over past 2 hours, 3 hours, and 6 hours, total fiber consumed over past 12 hours. This information also came from their food app.
HbA1c: A measure of long-term blood sugar control. This was measured at the beginning of the study.
Personal information: Physical activity duration and frequency, sleep quality, stress, and hunger levels throughout the day. This information came from their exercise phone app. BMI (a measure of obesity), age, gender, and regularity of defecation. This came from the questionnaire they filled out when they entered the study.
Continuous blood sugar responses before, during, and after each meal. This came from the glucose monitor the subjects wore for a week.

I went into detail in describing the modeling approach so you can understand how comprehensive the model was. This in not just some personalized testing protocol where you can just send off a stool sample for microbiome testing, a cheek swab for DNA testing, and/or fill out a diet and lifestyle questionnaire. This is the kind of personalized testing that could only be done in a medical center and would likely cost well over a thousand dollars.

Can Personalized Tests Help You Gain Better Control Of Your Blood Sugar?

Here are the key findings from the study.

The accuracy of this model for predicting the blood sugar response of individual subjects was around 60% compared to around 40% when the investigators just took into consideration the carbohydrate content of the meals.
Every component of the model contributed to the accuracy of predicting individual blood glucose response.

These findings led the authors to conclude that their model “…is a promising means for designing effective nutritional interventions to control glycemic [blood sugar] responses to foods.” This conclusion is what generated the headlines you may have seen.

What Are The Weaknesses Of The Study?

In many ways this was a very well-designed study, but it had two major weaknesses.

The day to day reproducibility of blood glucose predictions for the standardized bagel and cream cheese meal was only around 66%. That is disappointing for a very expensive test that can only be performed in a medical center.
The authors did not calculate the predictive value of glycemic index, which they could have easily done from their data. Since glycemic index is a better predictor of blood sugar response than carbohydrate content, this is a major weakness of the study. One is left wondering if this extensive and expensive test approach is significantly better at predicting blood sugar responses than simply using glycemic index as a predictor.

What Is The Truth About Personalized Nutrition Testing?

Here are the takeaways from this study:

Restricting carbohydrates is not a particularly effective way to control your blood sugar levels. Unless you completely eliminate carbohydrates, your chances of controlling blood sugar levels are only around 40%. And, if you do eliminate carbohydrates, your diet is deficient in nutrients, phytonutrients, fiber, and friendly gut bacteria. In short, it is a very unhealthy diet.
If the personalized nutrition testing protocol described in this study were commercially available, you could increase your ability to control blood sugar levels to 60%. That is an improvement, but…
You would need to continuously monitor diet, exercise, and blood sugar levels for a week as part of the testing protocol as described above.
The test would likely cost thousands of dollars and require that you travel to a major medical center with the capabilities to administer such a program.
We don’t know whether this testing protocol is significantly better at predicting your blood sugar response to various foods than simply relying on the glycemic index of those foods.
If you significantly changed your diet and/or lifestyle, this program would likely become worthless at predicting your blood sugar response. That is because the predictive ability of this program depends on the interaction of every component of your diet and lifestyle.

In short, this personalized nutrition program requires a lot of effort and expense for a slight increase in your ability to predict which foods cause your blood sugar levels to increase.

My Recommendations

If you want to keep your blood sugar under control, here are my recommendations:

Avoid “personalized nutrition tests.” The ones that offer any benefit are expensive and time-consuming. The slight advantage they offer is not worth your time and effort.
Start by eliminating sodas, sugary junk foods, and highly processed foods from your diet. That includes white flour and other refined grains. This one change will make a bigger improvement in your blood sugar control than anything else you can do.
Don’t eliminate whole food groups in an effort to restrict the carbohydrates in your diet. This is particularly true for fruits, legumes, and whole grains. They provide nutrients, phytonutrients, fiber, and support the growth of healthy gut bacteria that are essential for your good health.
If you have trouble controlling your blood sugar levels, choose carbohydrate foods with a low glycemic index.
Think in terms of meals rather than individual foods. A piece of chocolate cake will have much less effect on your blood sugar level when consumed as part of a meal containing protein, fiber, and healthy fats than when consumed as a snack.
We are all different. Learn to listen to your body. This is more important than personalized nutrition testing or anything else I have mentioned. Pay attention to the foods you eat.

If you consistently experience symptoms of hyperglycemia (high blood sugar) shortly after you eat a particular food, and/or symptoms of hypoglycemia (low blood sugar) a short time later, that food is not your friend.

It doesn’t matter that a personalized nutrition test said you could eat it. It doesn’t matter that the food has a low glycemic index. You should minimize that food in your diet.

Symptoms of high blood sugar: fatigue, thirst, headache, trouble concentrating, and frequent urination.
Symptoms of low blood sugar: hunger, shakiness, anxiety, irritability, feeling lightheaded, and sleepiness.

The Bottom Line

A recent study reported that a personalized testing program was 60% accurate in predicting an individual’s blood sugar response to various foods. That was slightly better than the 40% accuracy when the investigators just considered the carbohydrate content of the foods.

However:

The day to day reproducibility of blood glucose predictions for a standardized meal was only around 66%. That is disappointing for a very expensive test that can only be performed in a medical center.
The authors did not calculate the predictive value of glycemic index, which they could have easily done from their data. Since glycemic index is a better predictor of blood sugar response than carbohydrate content, this is a major weakness of the study. One is left wondering if this extensive and expensive test approach is significantly better at predicting blood sugar responses than simply using glycemic index as a predictor.

For more details and my personal recommendations on how to best control your blood sugar levels, read the article above.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.