Browse evidence-based analysis of health-related claims and assertions
Insulin by itself doesn’t change estrogen production in fat, but when it’s with cortisol, it makes the difference between men and women disappear.
Descriptive
After menopause, belly fat becomes more responsive to stress hormones by making more estrogen than before menopause.
In belly fat, cortisol makes both men and women’s fat cells make more estrogen, but it boosts it way more in men than in women.
In women, a stress hormone called cortisol makes fat tissue produce more estrogen, but in men, it does the opposite—this might help explain why women store more fat under the skin than men.
Unlike belly fat, gaining or losing fat around the hips didn’t seem to affect how likely women were to die or have heart disease over six years.
Correlational
Women who started at a normal weight or had smoked in the past were at the highest risk if their waist got bigger over six years.
Women who gained belly fat over six years were more likely to die or have heart problems later, even if they weren't overweight to begin with.
As people get older, their belly fat tends to increase — and this increase is a bit more clearly linked to age when measured with ultrasound than when just measuring the waist.
Just measuring your waist size doesn’t tell you as much about your blood sugar and cholesterol levels as an ultrasound scan of your belly fat does — even when you already know someone’s weight and age.
Measuring belly fat with an ultrasound shows a stronger link to bad blood sugar, cholesterol, and fat levels than just measuring waist size, even when you account for a person’s age, sex, and overall weight.
For women with PCOS, metformin lowers the male hormone testosterone — but only in those with PCOS, not in other obese women — showing it targets the root cause of symptoms like facial hair.
Causal
Metformin lowers leptin — the ‘satiety hormone’ — in obese women, even when they lose the same amount of weight as those not taking it, meaning it might directly affect how the body regulates hunger.
Eating fewer calories for a month helps obese women lose weight and shrink their waist, but doesn’t yet reduce the deep belly fat or the fat under the skin — that takes longer, like with metformin.
Even women without PCOS who are obese and take metformin with a diet lose weight and belly fat, and their SHBG (a hormone that binds male hormones) goes up — but their male hormone levels don’t drop like in women with PCOS.
For obese women with PCOS, taking metformin along with a low-calorie diet helps them lose more weight, shrink belly fat, lower male hormone levels, and get more regular periods than just dieting alone.
Having diabetes and having high visceral fat (measured by VAI) each add their own separate risk for heart problems in people with heart disease — knowing one doesn’t tell you everything about the other.
People with heart disease who also have type 2 diabetes are about 55% more likely to have a heart attack, stroke, or die from heart problems than those without diabetes — even when you account for other risk factors like weight and cholesterol.
People with heart disease who have more fat around their organs (measured by a simple formula using waist size and blood fats) are more likely to have serious heart problems like heart attacks or strokes, whether or not they have diabetes.
In people with obesity, the levels of receptors and enzymes for male and female hormones in fat tissue don’t seem to be linked to how much fat they have or where it’s stored.
In people with obesity, fat tissue that processes male hormones differently seems to be linked to having more fat around the waist.
In people with obesity, fat tissue that makes more estrogen seems to be linked to having more total body fat.
Some scientists thought that fat around the organs might make too much of the stress hormone cortisol locally, which could make people gain weight—but after looking at many studies, it seems this probably isn’t a big reason for obesity.
Losing weight—whether by eating better, exercising, taking medicine, or having weight-loss surgery—can help reduce fat, inflammation, and scarring in the liver of obese people with fatty liver disease.
Most people with fatty liver don’t feel sick, and their liver blood tests are often normal—so doctors can’t rely on symptoms or routine blood work to find it; they need imaging or to check for obesity and diabetes instead.