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Obesity Fact #1 Heritability is Not Destiny



Now that we have discussed the myths and presumptions, it is time to turn to what the authors of the New England Journal of Medicine paper consider to be “facts”.

These are statements about obesity, which the authors consider facts because there is sufficient evidence to consider them empirically proven.

As one may expect, “conclusive” evidence can only come from experimental studies (ideally, consistent findings from several well-designed randomised controlled trials, which constitute the highest level of evidence). Thus, it should come as no surprise that most of the facts identified by the authors pertain to issues that lend themselves to examination in such trials.

Obesity Fact #1 is that,

“Although genetic factors play a large role, heritability is not destiny; calculations show that moderate environmental changes can promote as much weight loss as the most efficacious pharmaceutical agents available.”

This fact is based on several studies that have shown that it is indeed possible to “modulate” genetic risk by changes to the environment (i.e. diet and exercise).

This finding is neither new nor limited to obesity. After all, even severe monogenic inborn errors of metabolism (like phenylketonuria) respond to changes in the environment (like elimination of phenylalanine in the diet).

However, it is important to remember that achieving lower weights for someone with a strong genetic disposition for obesity will always be so much harder than for someone without that genetic risk.

Thus, while environmental changes, which affect everyone, can perhaps reduce the average weight in a population, they will still leave the biggest people the biggest (albeit at a lower weight).

Just how big and feasible such environmental changes would need to be to significantly reduce obesity will remain to be seen.

At the individual level we have a fair idea that, for some people, this effort is likely to be substantial (readers may recall the recent series on Mark, Julie, Gertrude and Janice).

At an individual level there is certainly no doubt that some people are going to have to work much harder at trying to lose weight or keeping it off than others – so much at least, will always be destiny.

AMS
Edmonton, AB

5 Comments

  1. The paper they refer to support this fact is a review that describe several other papers. Most of the review emphasizes the lack of a role that environment plays in the weight status of young people, but does describe a paper indicating a role for environment in the weight status of people in middle age. Over a lifetime, the predicted effect of environment on weight is 12.2 pounds or a BMI change of 1.8. Most obese people would still be obese if they lost 12.2 pounds.

    It is not at all clear to me how this finding translates into the idea that “heritability is not destiny.” As you pointed out, for most inherited conditions we have some way to intervene to improve the outcome; the question is the degree to which we can improve the outcome. For individuals who are genetically predisposed to obesity, the reference would seem to indicate that we can only change the outcome for some people and we can only change it a little bit.

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  2. And what of the findings regarding identical twins who are adopted into different families? Hasn’t it been clearly established that a twin who is hereditarily predisposed to thinness will remain thin, even if s/he is brought up in a family of heavy folk and vice versa?

    Environment no doubt plays a role–in perhaps keeping the naturally fat from becoming extremely fat. However, to actually turn those whose genetic make-up predisposes them to being on the heavy side into thin people, inordinate amounts of exercise and an inordinately restrictive diet are required, as we have seen from the results of the National Weight Control Registry.

    If naturally slim people were forced to exercise as diligently and monitor their food intake with the same intensity as those who have lost weight must do to maintain their weight loss, they would stop blithely bandying about the “eat less move more” mantra. Probably 95% of them would find it just as untenable in the long term as the 95% of fat people who regain the weight they lose.

    I suspect you don’t realize just how much “weight” your own words hold when you say, “At an individual level there is certainly no doubt that some people are going to have to work much harder at trying to lose weight or keeping it off than others – so much at least, will always be destiny.”

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  3. “…it is important to remember that achieving lower weights for someone with a strong genetic disposition for obesity will always be so much harder than for someone without that genetic risk.”

    This is one of my foundational principles and a primary focus for my work and my writing! This is a key factor in dealing with the pervasive shaming and bias that exist in our culture. I believe that people approach weight management very differently when they can accept this fact and let go of all the self-shaming they can be driven to!

    Thank you, Dr. Sharma.

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  4. “At an individual level there is certainly no doubt that some people are going to have to work much harder at trying to lose weight or keeping it off than others – so much at least, will always be destiny.”

    Or we could, you know, just work with the bodies we have and not focus on weight at all. Trying to be thin isn’t destiny. It’s a choice, and one that doesn’t work out very well for most people who would need to lose and keep off more than 20 or 30 pounds to get there. Better to focus on health, if that’s a concern, or to focus on living well and contributing something to society.

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  5. Obesity fact 1 may be true but is very misleading. This is because the typical amount of weight lost (other than via bariatric surgery) across hundreds of well supervised trials is about 5% of body weight, whether drugs are used or not.

    This is certainly not strong evidence that the high heritability of weight, of around 80%, compared with around 90% for height, is likely to be overcome. Except for individuals with high levels of obsessive-compulsiveness (like the NWCR ‘long term weight loss maintainers’, judging by their reported behaviours) the probability of permanent weightloss beyond about 10% of body weight is very low indeed. While the health benefits of small weightloss are great, a loss of 5-10% won’t change the individual into a thin or normal weight. To imply, as this ‘fact’ does, that people can readily overcome their genetics is cruel and misleading. As DeeM has said, it would be much better to focus on health and contributing to society.

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