Credit: Illustration by Slug Signorino

People diagnosed as clinically obese are sometimes said to have a hormonal condition that makes them unable to lose weight even if they cut calorie intake to a minimum. Surely if you forced them to exercise while making certain their dietary intake and vital signs were healthy, they’d be slim and trim in a couple years. In the end, isn’t obesity always in the mind and not in the hormones? —Guy

I see you’re an adherent of the suck-it-up school of clinical analysis, Guy, which is my default attitude too. Overweight? Eat less and exercise more. Nervous and depressed? Get a grip. Spurting carotid artery? Nothing some finger pressure and a butterfly bandage won’t solve. However, not everybody shares our gritty pioneer spirit. Thus we’re obliged to plunge into the research literature. Not to worry: the laws of the universe are on our side.

There’s no denying your main point: people lose weight when they burn more calories than they consume. It’s the first law of thermodynamics—no matter what you hear about low-calorie intake leading to metabolic shutdown, energy must be conserved. While outright coercion may not be the best way of going about it, you can make anyone lose weight if you get the input-output balance right.

The problem is your assumption that a medical condition is just an excuse. Sometimes it might be. But not always. Many medical problems can lead to weight gain, and some of these can legitimately be described as hormonal conditions. One relatively common example is hypothyroidism, which afflicts about five percent of the population. Essentially your metabolism slows down. You become less active, and assuming your eating habits stay the same, you gain weight.

Polycystic ovarian syndrome, or PCOS, which affects 7 percent of women, can also lead to weight gain for reasons that aren’t clear. Many women with PCOS are insulin-resistant: their cells don’t absorb glucose as readily as they used to, and the excess gets stored as fat. Insulin resistance, which can lead to diabetes, is a fairly common problem linked to obesity. But it’s simplistic to say insulin resistance makes you fat. On the contrary, though much remains to be learned, resistance is generally thought to be the effect rather than the cause of weight gain.

After that, relevant hormonal conditions get scarce pretty fast. Cushing’s syndrome, caused by abnormally high levels of the hormone cortisol, can lead to specific types of weight gain including a round “moon face” or a “buffalo hump” of fat on the neck and upper back, but fortunately it’s rare.

Sometimes medications can lead to weight gain. For example, about half of schizophrenic patients and two-thirds of bipolar disorder sufferers are obese due to a combination of illness-related factors and side effects from their antipsychotic medications. Depression can lead to obesity, and so can antidepressants, many of which list weight gain among possible side effects (although most manufacturers report that weight loss is more common). Those who take corticosteroids for asthma or other problems can put on weight as well. If these people stopped taking the problematic medication I guess they could lose weight, but which would you rather be, fat and happy or thin and sick?

Is obesity genetic? Maybe in part. Research suggests 16 percent of the population has a version of the fat-mass- and obesity-associated gene, known as FTO, that increases one’s propensity to put on the pounds. However, the amount of extra weight attributable to this gene is small, just seven pounds on average. Likewise, a few overweight folks have problems with their leptin receptor genes, which can lead to early obesity by suppressing the signals that tell the body it’s had enough to eat. Roughly 10 percent of us have an insulin-affecting gene that increases the risk of obesity.

Still, while medical or genetic conditions play a role, most serious students of the obesity epidemic are lining up with you, Guy. The percentage of meals eaten away from home has doubled since 1978; during roughly the same period, the average U.S. food intake has increased by 200 calories per day. Our ability to judge what food will do to our waistlines is notoriously bad. In one 2006 study, 193 consumers were asked to estimate the calorie content of an order of cheese fries with ranch dressing. Average guess: 869 calories. Actual damage: 3,010 calories.

Today, one U.S. adult in three is obese, more than double the rate in 1980. You can’t blame hormones for that drastic increase. Do we chalk it up to the public’s pathetic lack of willpower? My inner puritan says yes. However, there’s no question that the masses are being hammered by an ever-present voice asking, “You want fries with that?” —Cecil Adams

Is there something you need to get straight? Take it up with Cecil at straightdope.com.