Author: Dr. Stephen Chaney
It is so confusing. The weight loss claims for popular diets sound so convincing, but they can’t all be true.
The low carb proponents give impressive metabolic arguments for why their diet works best. (Of course, you aren’t a biochemist. You have no idea whether they are speaking the truth or just trying to pull the wool over your eyes.) They quote clinical studies and offer testimonials that “prove” their diet works.
Other “experts” tell you that is nonsense. Your diet needs to be individualized to fit your genetic and metabolic profile. Who do you believe? Do low-carb or low-fat diets work better? Are individualized diet plans the solution?
Fortunately for you a recent study (CD Gardner et al, JAMA, 319: 667-679, 2018 ) has answered your questions. Let me start with some background to put this study in perspective. Then I will describe how the study was done, the study results, and what this study means for you.
What Did We Already Know About Diets?
The studies that low-carb proponents quote to “prove” the success of their diet approach are misleading because:
- Most of the studies are short-term. This is misleading because low-carb diets lead to an initial loss of water weight that is not seen with low-fat diets.
- Most of the comparisons are done with the typical American diet (which is high in sugar, refined carbohydrates, and junk food) rather than a healthy low-fat diet.
- Note: This is the short version. I cover this in more detail in my new “Slaying The Food Myths” book.
In contrast, there have been numerous studies comparing the effectiveness of low-carb versus low-fat diets long term (12 months or more). These studies have not found a dimes worth of difference between the two diets. Weight loss was virtually identical.
That has led some weight loss experts to point out that any “one size fits all” diet fails to account for individual variability. They point out that while average weight loss on a particular diet might be 12-15 pounds, some people will have lost 45 pounds and others gained 5 pounds. That has led to research efforts to discover biomarkers that could predict which diet will work best for you. Let me share the two most promising approaches.
A DNA testing approach measures genetic variation in the PPARG, ADRB2, AND FABP2 genes [Don’t worry. There won’t be a quiz.] These are genes involved in fat and energy metabolism. Animal studies have suggested that genetic variation in these genes might be useful in predicting whether individuals respond better to a low-fat or low-carb diet. One preliminary clinical study has suggested it may work for humans as well.
An insulin sensitivity approach measures insulin levels 30 minutes after a glucose challenge (a measurement called INS-30). Some small clinical studies have suggested this approach might also have value in predicting the success of low-carb versus low-fat diets for weight loss.
Unfortunately, some companies are already promoting individualized diet plans based on DNA testing and insulin sensitivity measurement – even though the clinical support for the predictive power of those tests is very preliminary at present.
The current study was designed to compare the effectiveness of healthy low-carb and low-fat diets on weight loss. In addition, it evaluated whether either DNA testing or insulin sensitivity measurements could effectively predict whether individuals lost weight better on low-fat or low-carb diets.
How Was This Study Done?
This was an excellent study. In fact, it is one of the best studies comparing weight loss diets I have seen in recent years. It enrolled 609 middle-aged (average age = 40), overweight (average BMI = 33) adults from the San Francisco Bay area in a 12-month weight loss study. Here was the breakdown of participants:
- 57% were women, 43% were men.
- 40% had a DNA pattern considered favorable for a low-fat diet, 30% had a DNA pattern considered favorable for a low-carb diet (30% had an intermediate DNA pattern that did not predict either low-carb or low-fat).
- 67% had insulin sensitivity values considered favorable for low-carb diets, 33% had insulin sensitivity considered favorable for a low-fat diet.
The study participants were randomly assigned to either the low-carb diet group or low-fat diet group by a computerized protocol that assured DNA patterns and insulin sensitivity were equally distributed across the two groups.
In contrast to many earlier studies, both groups followed a relatively healthy diet. They were instructed to:
- Maximize vegetable intake.
- Minimize intake of added sugars, refined flours, and trans-fats.
- Focus on whole foods that were minimally processed, nutrient dense, and prepared at home whenever possible.
The participants were not advised to restrict their calories. However, they were given an extraordinary degree of support. They were further divided into groups of 17 that met a total of 22 times over the 12 months with a registered dietitian who provided instruction, support and encouragement. That level of support assured that the participants stuck with their diet for the full 12-month period.
Can Genetics Predict Which Diet Works Best?
Participants in the study lost an average of 12 pounds. That is not a huge amount of weight, but it is enough weight loss to make a difference, and it is consistent with the results of most long-term studies. When the results were broken down further:
- There was no significant difference in weight loss between the low-carb group and low-fat group at 12 months. This is consistent with multiple previous studies.
- Both diets were equally effective at improving lipid profiles and lowering blood pressure, insulin, and blood sugar levels. This is the dirty little secret that many low-carb enthusiasts don’t tell you. The improvements seen in health parameters such as lipids, blood pressure, insulin, and blood glucose are due to the weight loss, not whether the diet is low-carb or low-fat.
- Neither the DNA pattern or insulin sensitivity offered any predictive value as to whether a low-carb or low-fat diet was more effective for weight loss.
That does not mean that DNA testing is of no value. It simply means that the human genome is far more complex than the companies offering DNA tests have assumed. There will be a day when we know enough to individualize diets based on DNA testing. That day is not now.
What Does This Mean For You?
Forget the weight loss claims of the low-carb enthusiasts. Ignore companies that promise they can select the best diet approach for you based on some simple DNA tests and/or measurements of insulin sensitivity.
This study does not provide definitive answers, but it hints at the weight loss tips that really matter:
- Ditch the sodas, sweets, fast and processed foods. Instead focus on whole foods, primarily fruits and vegetables, whole grains, and legumes.
- If you wish to follow a low-carb diet, choose one that is primarily plant-based rather than meat-based.
- Focus on what you are eating rather than on calories.
- Find a group to provide support and encouragement. It doesn’t need to be some expensive diet program. It could just be a group of friends who agree to provide each other with support, encouragement, and accountability.
I cover this topic in much more detail in my new book “Slaying The Food Myths”.
The Bottom Line:
A recent study compared the effectiveness of healthy low-carb and low-fat diets on weight loss over a 12-month period. In addition, it evaluated whether DNA testing or insulin sensitivity measurements could effectively predict whether individuals lost weight better on low-fat or low-carb diets.
- There was no significant difference in weight loss between the low-carb and low-fat groups at 12 months. This is consistent with multiple previous studies.
- Both diets were equally effective at improving lipid profiles and lowering blood pressure, insulin, and blood sugar levels. This is the dirty little secret that many low-carb enthusiasts don’t tell you. The improvements seen in health parameters such as lipids, blood pressure, insulin, and blood glucose are due to the weight loss, not whether the diet is low-carb or low-fat.
- Neither the DNA pattern or insulin sensitivity offered any predictive value as to whether a low-carb or low-fat diet was more effective for weight loss.
That means you can forget the weight loss claims of the low-carb enthusiasts. You should also ignore companies that promise they can select the best diet approach for you based on some simple DNA tests and/or measurements of insulin sensitivity.
As for what works and why, I cover that in detail in my new book “Slaying The Food Myths”
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.