What causes obesity?

Gretchen Becker Health Guide
  • Sometimes it seems as if almost every other day there’s a new press release about what causes obesity. And when there are many different theories of some medical puzzle, it usually means that no one has found the answer yet.


    I think those who read shareposts on this site understand that there’s more to being overweight than just eating too much and not exercising enough. A lot of people have those unhealthy behaviors and maintain a normal weight with no effort. They’re basically just lucky. And sometimes a person who eats nothing but junk food and spends all day in front of a computer maintains a normal weight when young but then gains a lot of weight when middle age arrives.

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    One recent study concluded that there’s a strong genetic component to both diabetes and obesity, which are linked, but the genetic component isn’t simple. There’s not one “obesity gene” or one “diabetes gene.” They suggest that many different genes can be involved, and many of these genes are rare. That makes them more difficult to find.


    It also means that different patients have different defects and will react differently to treatment. We patients call this YMMV, or “your mileage may vary.” The best treatment for me might not be the best treatment for you.


    The genetic component also interacts with the environment, making study of the problem even more complex.


    “The reason we see so many people getting fat is that they carry strong hunger genes while the environment is maxed; it’s an obesogenic environment that rewards eating,” said professor Lesley Campbell, the lead researcher of the study. He said that a previous study showed that “people with diabetes in the family tend to be hungry more often, are able to eat more at a sitting, and will generally opt to eat high-calorie foods. This does not mean they are ‘greedy,’ it just means that their bodies are genetically driven to eat more.” And when food is plentiful, that’s what they’ll do.


    “The same genes would serve these people well in times of food scarcity or famine. They would survive, while their leaner neighbors would perish.”


    Another recent study explored the problem of why some people eat more than others. One answer: they’re hungrier.


    These researchers looked at the hormone ghrelin, which the stomach produces when it’s time to eat. After you eat, the ghrelin levels usually fall. So logically, one might expect that people who eat a lot produce more ghrelin.


    But that doesn’t seem to be true. Plasma ghrelin levels in overweight people are normal, or even subnormal. So then why are they hungrier than normal?


    It turns out that overweight people produce an antibody against ghrelin. This antibody binds to ghrelin and keeps it from being broken down when it should be; the ghrelin persists much longer than normal, so you’re hungry much longer than normal-weight people.


    And an Australian study looked at why it’s so difficult to keep your weight off after you’ve lost it. These researchers, working with mice, found that when they made mice fat with a “high-fat diet,” the nerves in the stomach that are triggered when the stomach fills with food were desensitized. Normally, when we eat, the expansion of the stomach triggers nerves that tell the brain that we should stop eating.


    Note that when researchers give mice a “high-fat diet,” they usually use a regular chow diet to which fat has been added, and this is an easy way to make the mice obese. The results from such a diet may be different from a high-fat low-carb diet in humans.


    But in mice on the obesity-causing high-fat diet, at least, the decrease in sensitivity of the stomach nerves was long-lasting. When they made the mice lose the extra weight, their nerves continued to be desensitized. They don’t know if the change in the nerves is permanent or just long-lasting.


    If the mice studies translate into human physiology, it would mean there are at least two reasons you might be hungrier than other people. The ghrelin makes you start eating because of hunger and the compromised nerves fail to tell you to stop eating once you’ve begun.

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    Finally, a fourth study  explored the question of why some people seem to gain weight even when they don’t eat more than people who are thin. Again, your genes can be involved. The researchers found a gene in mice (with a human counterpart) that made the mice gain more weight than other mice even when they didn’t eat more food. The mice had to eat 10% to 15% less than the control mice in order to maintain their weight.


    The researchers note that the particular mutation they studied is rare, found in less than 1% of overweight people. It can’t explain every case of obesity. But they suggest that there are probably other similar genes that do the same thing.


    When you go to your doctor and say you’re following a prescribed diet to the letter but you’re not losing weight, the doctor may assume you’re not telling the truth. But, as discussed in an article in the New York Times, maybe you are.


    Interestingly, when the mice in this study were young, they ate just as much as their siblings but gained more weight. But when they became obese, they not only continued to gain weight, but their appetites also increased, a double whammy.


    What all these studies suggest is that it’s very difficult to become slim and stay slim when your genes are stacked against you. We already knew that, of course. But if scientists can find out for sure what is most important for most people in order to lose weight and keep it off, the lives of millions of people would be improved.


    Weight loss will reduce insulin resistance, and this usually improves diabetes control. But not always. It depends on whether your primary problem is insulin resistance or a lack of insulin. There are many annecdotal reports of people who lost more than 100 pounds, and although they felt better and had better blood pressure, the weight loss had no effect on their diabetes control.


    Does that mean you should stop trying to lose weight? Definitely not! When you weigh less, it’s easier to exercise, and exercise has a beneficial effect on your heart disease risks, which are usually elevated when you have type 2 diabetes. Weight loss also usually reduces blood pressure, and high blood pressure increases heart disease risk almost as much as uncontrolled diabetes.


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    Finally, if you lose weight, you’ll usually feel a lot better about yourself, and stress is a major cause of all kinds of health problems.


    So hang in there! Do what you can to lose weight and keep it off. But if it’s impossible for you, don’t beat yourself up about it. It may not be your fault.

Published On: November 15, 2013