Four Hidden Factors That Control Your Weight

You have probably heard that weight is a matter of “calories in versus calories out.” If you eat more than you burn, you gain weight, right? Wrong. Weight is NOT just about calories in versus calories out.

This is important information, because people with diabetes are usually told to lose weight. This advice rarely helps, because weight depends on several factors that vary widely and are largely out of our control. The advice should be: move more, eat healthier food, reduce stress. If you lose weight, fine. If you don’t, that’s OK, too.


In the broadest, least meaningful sense, calories in versus calories out contains some truth, but it’s only a tiny part of our bodies’ weight setting. Here are four of the other factors controlling weight:

1. Intestinal bacteria influence how our bodies process food. Scientific American published reports indicating that “Gut bacteria alter the way we store fat, how we balance levels of glucose in the blood, and how we respond to hormones that make us feel hungry or full. The wrong mix of microbes, it seems, can help set the stage for obesity and diabetes from the moment of birth.”

We inherit our original gut bacteria from our mothers. Thin people tend to have a greater variety of bacteria called Bacteroidetes in their guts. Bacteroidetes are germs that can break down plant starches and fibers. If you have a good number of Bacteroidetes, you can eat more fiber and break it down for energy and other functions. Without good bacteria, your body won’t like fiber and will crave refined carbs like sugar.

In one rodent study reported by Scientific American, mice were raised in a sterile environment, and then fed bacteria. The donors were four sets of twin human sisters, one thin and one fat in each pair. “The mice ate the same diet in equal amounts, yet the animals that received bacteria from an obese twin grew heavier and had more body fat than mice with microbes from a thin twin.”

2. Metabolic rate — what does “calories out” mean? The rate of base metabolism, or BMR (how much energy a body uses at rest), varies widely between people. Medscape lists several factors controlling BMR. These include thyroid hormones and “catecholamines” such as adrenaline. Body temperature makes a big difference, and many of these factors seem set by our genes.

BMR accounts for roughly 60% to 75% of our total energy output. According to Medscape, we don’t know if or by how much BMR can be altered. So probably only about a third of “calories out” are under our control.

One thing that does alter BMR is cutting calories in. The National Institute on Aging has found in several studies that restricting calories slows your BMR. Reducing calories “in” automatically reduces calories out, a major reason why dieting usually fails to provide lasting weight loss.

3. Insulin function. Insulin resistance makes it highly probable that you’ll store more fat than you need. The site Lifetime Weight Loss makes a very good point: “You’ll be unsuccessful at losing fat if you don’t burn fat,” they say, “even if you eat fewer calories and burn more through exercise. You can lose weight, but most of the loss will come from lean body mass, or muscle tissue, not fat.” That’s because high levels of insulin, commonly seen with insulin resistance, increase the storage of fat in fat cells. Insulin prevents the cells from releasing fat for energy.

4. Environmental chemicals have a huge influence on weight. They can stimulate fat cell growth, change digestion, and increase appetite. As you can read here, these chemicals include persistent organic pollutants (POPs), air pollution, pesticides, and phthalates used in some plastics. A 2006 study in the journal Diabetes Care found that obesity did not increase the risk of Type 2 diabetes in obese people with very low levels of POPs in their bodies.

An editorial comment by a Spanish doctor in The Lancet stated, “This finding would imply that virtually all the risk of diabetes conferred by obesity is attributable to persistent organic pollutants, and that obesity is only a vehicle for such chemicals.”

You can see more about the effects of chemicals such as estrogen-like compounds, antibiotics, and fungicides like tributyltin in this article. It’s called “Why Are Animals Getting Fat?” Hint — it’s not because they are exercising less.

None of this means you shouldn’t exercise more or try to eat better. Those things will help you enjoy life and feel better. It just means the effects of these behaviors on your weight are uncertain. Don’t let people shame you with calories in, calories out. Show them this article.

One thing I still believe is the value of increasing fiber intake. It might be hard at first, but more fiber will lead to better gut bacteria, a more moderate insulin response, less insulin resistance, and hopefully less absorption of toxic chemicals. Remember to drink more water to keep the fiber soft.

  • Marilyn Wann

    The urge to blame 100% of various health concerns, and especially diabetes, on fat is inspired largely by anti-fat stereotype and stigma and prejudice, not by science. I appreciate the skepticism this writer shows about the hate-based equations: fat=bad and fat=unhealthy. Such resistance to the socially sanctioned weight-blaming is in dire need for both public health and social justice. However, I am sure there are other powerful confounding variables that influence individual and population weights. Some that come to mind: levels of brown fat, other genetic predispositions, poverty, history of weight cycling due to weight-loss attempts, and weight-related side effects from commonly prescribed drugs such as anti-depressants. Also variables that we think of positively: reduced levels of starvation, increased access to vaccines and antibiotics and prenatal/early child care. – Marilyn Wann

    • RAWLCM

      Marilyn, you are so right. Overweight people are the last minority that it’s socially acceptable to hate and discriminate against. And if it were as simple as diet and exercise, there wouldn’t be world-class athletes with metabolic syndrome, who struggle to keep weight off despite rigorous training and supervised diet programs.