It’s common knowledge that if you want to lose weight, you should just limit yourself to 1,200 calories a day. Health and fitness sources nearly universally recommend this number. At this level of sustenance, they claim, the body can burn fat without any detrimental side effects. In the short term, it’s true that eating 1,200 calories a day will likely result in weight loss, just as any reduction in calorie intake probably will, but it isn’t that simple.

University of Minnesota students are undoubtedly aware of the 1,200 calorie guideline. In my four years on campus, I’ve come across many students — especially women — who are constantly limiting themselves to 1,200 or 1,500 or some other low number of calories. And not just for a short time.

Many of them have been doing so since I met them months or years ago. But these consistent low-calorie eaters almost never need to lose weight. Rather, they are most likely to be those with little or no excess weight to lose. I’m not just talking about anorexia here. There are many students, men and women, who eat far too little without meeting the criteria for any medical condition.

It seems that we’ve taken the simple precept that fewer calories means less weight and used it to reach the unfortunate conclusion that permanently eating very few calories is a good, even healthy, way to maintain an ideal bodyweight.

It isn’t.

The body needs a certain minimum number of calories just to function properly and, more importantly, to be healthy. For most women, that minimum number is about 1,200 calories; for men, it’s about 1,500. Yet we need hundreds more calories (even thousands for very active people) each day to make up for all the movements we make — showering, walking across the Washington Avenue Bridge, exercising and doing homework all contribute to higher caloric needs.

When chronic under-eaters deny that need for more food, they’re at a higher risk for physical and mental damage in the long term. Loss of bone density, dry hair and skin, a weakened heart and hormonal imbalances are common physical manifestations of calorie deficiency.

Mentally, depression, anxiety and obsessiveness can also occur. These are only a few of the possible effects of dieting for months or years at a time, and there are many others.

It’s well established that eating too little is unhealthy, but the low-calorie mindset can be very difficult to escape. It’s common to fear that eating more than 1,200 calories — or some other arbitrarily low number of calories — daily will cause weight gain.

And weight gain may also occur in the short term — not because you’ve suddenly begun eating too much, but because calorie deprivation has damaged the body’s hunger and metabolism cues. Registered dietician and blogger Robyn Coale refers to this as “metabolic hibernation,” in which the dieter’s body begins packing on all the food the dieter eats because it thinks there’s a food shortage.

But over time, with an appropriate number of calories and a generally healthy diet, chronic under-eaters can begin to heal the physical and mental damage of long-term under-eating. With a normal metabolism and a moderately active lifestyle, the average college student needs far more than 1,200 calories.