You may have followed the same diet program as a friend, but they lost dramatically more weight, or performed the same training program and they experienced substantially better outcomes. Sure this is frustrating, but it's actually not surprising as we begin to understand the importance of individual variability in response to various lifestyle behaviors such as food intake and exercise.

It's not all bad news either.  If you didn't respond positively to a specific diet, supplement, or exercise program it just means you don't have the right genetic make-up for that particular program, but you have a blueprint more suited to something else. It's just a matter of finding the right one, which requires self-experimenting.  

Studies on Twins Reveal a Genetically
Predisposed Response to Exercise and Diet

Let's take a closer look at some of the evidence showing variability in response to diet and exercise.  Arguably the best proof showing the genetic contribution to the variability in weight loss comes from studies in monozygotic 'genetically identical' twins because this controls for genes. If there is a strong genetic component in a response variable you would tend to see the twin pairs respond exactly the same, but there would be differences between twin pairs.

Drs. Claude Bouchard and Angelo Tremblay conducted some very provocative experiments in the '90s that examined the variability in changes in body weight in response to negative and positive energy balance in relation to genetics. These were remarkably well-controlled studies conducted in a metabolic ward where they had precise control over food intake and exercise monitoring.  

In the positive energy balance experiment, identical twins were overfed 1000 kcal/day (6 days out of 7) for 100 days. There was a wide discrepancy in weight gain ranging from about 9 to 30 pounds between the different pairs of twins, but weight gain within each twin pair was quite similar. Specifically, the between twin variance in weight gain was three times the variance within pairs. When looking at gains in upper body fat or abdominal visceral fat, the between twin variance was six times greater than within pairs.

In the negative energy balance experiment, twins exercised twice a day (9 days out of 10) for 93 days, while holding each individual's intake at their sedentary maintenance energy level. This created a daily deficit of 624 kcal/day for everyone in the study. Similar to the weight gain findings, there was a surprisingly wide discrepancy in weight loss among the different pairs of twin ranging from 2 to 18 pounds, while weight loss within twins was again very similar.

Can you imagine exercising for 2 hours per day and only losing a couple pounds. It's not the twins fault, they just don't have the genetic blueprint to lose weight in response to doing a lot of exercise. But that doesn't mean they wouldn't be responsive to other approaches to weight loss.  

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These well-controlled prospective twin studies demonstrate a remarkable level of variability in weight and fat loss between twin pairs. In contrast, the much smaller variance in changes in weight, especially fat mass, within twins provides convincing evidence for the role of genetic factors in determining how our bodies respond to both energy deficit and energy surplus.  

What this means is that genes have a major role in how you respond to diet and exercise. It is possible, for example, that if you exercise vigorously you may see very little benefit in terms of weight loss, but you may be programmed to be responsive to other approaches like carbohydrate restriction or targeted supplementation. Again the bottom line here is that until there are tests available to determine which diet and exercise program you are best suited for, it makes an enormous amount of sense to sensibly self-experiment and try various approaches to determine what works best for you. 

Have you tried a popular diet or exercise regimen that didn't seem to be working for you? How long did you stick with it? Let us know in the comments field below!

Bouchard, C. and A. Tremblay, Genetic influences on the response of body fat and fat distribution to positive and negative energy balances in human identical twins. J Nutr, 1997. 127(5 Suppl): p. 943S-947S.

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