How obesity is like nearsightedness


Modern life doesn’t play well with our ancient genes
copyright Jon Bunting

If your parents are nearsighted (or short-sighted, if they happen to be British), you’re likely to be nearsighted too. The heritability of this problem is as high as 90% in some twin studies. But that’s only true if you and your parents or siblings grow up in a similar environment.

When you shift to a different lifestyle, the outcomes change. In 1974, a team of researchers evaluated a community of Inuit in the Canadian Arctic soon after formal schooling was introduced. Of adults over 30, only a small fraction (4.5%) were nearsighted. In contrast, 45% of younger adults, ages 15-29, were nearsighted – a tenfold rate increase, which happened much faster than genes in the population could vary.

The increase in nearsightedness that struck the Inuit in one generation has spread all over the world. The US rate went from 25% in the early 1970s to 42% three decades later. In a few societies, nearsightedness rates are now nearly as high as they can get. Among modern Chinese students in Singapore, 90-95% are nearsighted.

Research in lab animals and epidemiology in people suggest that the culprit is too much time spent indoors. Weak artificial light does not provide the signals that the developing eye needs to grow to the right size.

Do these rapid changes mean that genes don’t matter to nearsightedness? Not at all. Children with a genetic predisposition are more likely to become nearsighted – or more severely nearsighted – than children whose parents have good vision.

Here’s one way to think about it. Picture 100 children lining up to receive their portion of nearsightedness. In an environment where kids spend all day outside, there’s only a small amount available, enough for the first three or four children in line. The rest get normal vision. In Singapore, there is a huge amount of nearsightedness, so the first few kids get a lot more, and there’s still enough left for almost everyone to get some.

In both cases, the kids line up in the same order, which is determined by their genetics. Regardless of the environment, the children at the front of the line (the most vulnerable) do worst, and those at the back of the line do best. But the amount of outdoor time determines how far down the line the problem is distributed.

Obesity has also increased in the population much faster than genes could change. Weight is as heritable as height. And like nearsightedness, weight is influenced by the environment, with the strongest effects on the genetically vulnerable.

Scientists don’t yet know which environmental changes are most important for the increase in obesity. Candidates include processed foods, antibiotics, stress, sleep loss, prescription drugsreduced exercise, and decreased cigarette smoking, among others. Whatever has changed over the past 50 years, it probably isn’t our collective willpower.

So why do we treat nearsighted and obese people so differently? You wouldn’t tell a person who wears glasses, “Well, it’s your own fault. You should have played outside more as a child.” But even health care professionals tend to blame their patients for being overweight, though they should know how powerfully the body fights against weight loss.

Maybe it’s time to rethink our cultural focus on individuals and their willpower as the cause of weight gain. In addition to being more fair, concentrating on the bigger picture might give us some ideas that actually work to promote health and fitness.

14 thoughts on “How obesity is like nearsightedness

  1. Pingback: Comparing Obesity to Near-sightedness | MerrieBelle – Learning to Live Healthy & Loving My Life

  2. I’m so glad you are writing and speaking about this (I can’t wait to see your TED talk!). I’m afraid things are going to get far worse for overweight folks before they get better (e.g., companies that punish or reward employees for their BMI).

  3. The analogy works half-way but then breaks down. I can change my environment (change the profile of what I eat) and lose weight. In fact, I reduced from 190 to150 pounds, where I have remained for over six years now. However, I am far-sighted and as far as I know, there is nothing I can do to change my environment to restore 20-20 vision.

    • I’m glad you were able to lose weight and keep it off, but a huge quantity of research shows that weight loss is temporary for the vast majority of people. Regain is the rule; your experience is the exception.

  4. Your timing is amazing. I’m staying with an aunt who argued with me very strongly that it can only be eating too much or not exercising enough. Nothing else can cause weight gain. An overweight person herself (who by the way gained weight on prescription drugs) she puts her gain down to enjoying the occasional ice cream. There is such a complete and utter refusal to listen to alternatives that I shut the conversation down and know that this topic is off limits from now on.

    Maybe you can put a facebook link on your posts – just a thought!!

  5. The level of Insulin resistance in an individual and how much carbohydrates (includes sugars) you consume will determine how fat you become.

    At any level of insulin resistance if you replace the carbohydrates and sugars with healthy fats you will lose weight and avoid diabetes.

    Dr. Elliot Proctor Joslin discovered this in 1893. It still works today.

    • In long-term studies, low-carb diets show similar rates of regain to any other type of diets. People lose weight temporarily on almost any diet. It’s what happens later on that should concern us.

  6. Feed a child carrots and it will grow up liking carrots. Feed a child McD frys, and it will grow up gorging on frys.What we like is not strictly genetic, it is programmed by the environment. What has changed is having money to buy what manufactures line the supermarket aisles with, to wit, biscuits, cakes, tarts, mars bars and beer. When I was growing up, it was truly a treat to have apples and oranges at Christmas, because we could not afford them at other times. It is truly that simple. Diets do work, people that diet, loss weight. This is a proven fact. period. It’s when they stop dieting that they gain the weight back. Dah… The “eat food” set-point is just another, non genetic, adaptive characteristic that has been set wrong, and needs to reset to something sensible. dah… Oh… the argument about swapping near sightedness to fatties can equally be swapped to alcoholics. Is it more ok for fatties to stand outside a school eating a 24″ pizza that it is for an alcoholic to sit on the floor swigging whisky? If you take away responsibility for fatties being fat, that identical argument must also be valid for murderers. Remain=Input-Output. End of story.

    • You’re right about some things, wrong about others. It’s true that people’s taste preferences are strongly influenced by their childhood experiences, starting even before birth. Adult weight is also influenced by early experiences – but not the same ones. It’s also true that people who diet often lose weight. But that weight loss is temporary in almost all cases because the brain fights back against weight loss. Even people who try hard to remain on a diet for the rest of their lives usually gain the weight back. That’s not because they lack willpower but because their metabolism is suppressed and their hunger has increased dramatically.

      Obviously if people could lower their set points at will, they would lose weight and keep it off more easily, but that’s about as sensible or helpful as saying that alcoholics wouldn’t have a problem if they’d just stop drinking. Or that murderers should just stop killing people, I guess. Trust me, all those people already know that you disapprove of their behavior, and that hasn’t helped anything. Hating them harder isn’t going to help either, if you have any interest in being constructive.

      • The non debatable reason as to why people are fat, is because they eat to much. Period. Simple, indisputable laws of physics. The reason that over the last 50 years or so, the USA/UK have gotten fatter is because people only now have the money to buy any amount of food the manufacturers supply. It’s that simple. DNA has not changed in 50 years to even remotely explain the massive increase in obesity, and animals have never evolved to deal with unlimited food supplies. A key component as to why people remain fat is because evolution programs people to copy that which is already well copied. Evolution creates the assumption that if their are lots of something, it should be evolutionary successfully, so copy it some more, even if the assumption is wrong. Fat has reached critical mass. It is now deemed acceptable to be fat, simply because there are so many fat people, irrespective that it costs the UK NHS £40B a year, subsequently stopping children with leukaemia getting the best treatment that that money would buy.

        Sure, in the true, big universal scheme of things no one is responsible for anything they do, as it is trivial to prove that free will does not exist. e.g

        However, society would collapse if we all took that view. So, there needs to be an operational view, that assigns a pseudo freewill responsibility. For example, we lock up paedophiles, despite the fact that there is no realistic way that they can control themselves. From an operational view, there is no rational way to declare that those that get fat should be given protection not afforded to paedophiles in terms of responsibility of their actions. In the UK, smokers cost the NHS around £5B, however, the pay back £20B in tax. Fat people are a tremendous drain on society. That is reality, not hate. From what I skimmed from your book, it comes across as an apologist book attempting to legitimise away all responsibility.

        • You seem to have missed the point of the nearsightedness analogy. I agree that DNA hasn’t changed in 50 years, and that the environment has changed quite a bit, in a way that encourages weight gain. My point is that people’s genetics determine which of us will gain weight under those circumstances, and that changing the environment is likely to be much easier than changing the biology of how people respond to that environment. You’re in good company, though. Most Americans also don’t understand the science behind weight gain.

          Your comments suggest that you think fat people are analogous to alcoholics, pedophiles, and murderers, but you don’t feel yourself to be prejudiced against them in any way. That seems unlikely to me, whether or not you’re aware of your bias. But in any case, as a practical matter, the results of shaming or blaming people for their weight is very consistent in the research literature: it leads to further weight gain and damages health. (You can find the many references supporting this statement in my book.) So if your only motivation is a high-minded concern for the health care budget, your actions are in opposition to your stated goals.

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