It's a pretty simple formula when you think about it — if you eat fewer calories than you burn, you should lose weight. For most healthy adults that's sound logic, but sometimes we want to take it too far and eat even less.

The result, experts say, can have detrimental effects on the body, including slowing down weight loss rather than accelerating it. That's why the latest recommendations of a minimum of 1,200 calories per day for women and 1,500 for men are considered safe when it comes to weight loss. To take in fewer calories than that is considered undereating.

The Body And Undereating

The difference between fasting and undereating is important. Fasting is typically done over a period of several hours and — despite negative reports about some fasting or detox diets — can be effective for weight loss. Think of it this way: Your body is already set up to handle some fasting when you consider that we sleep eight hours a night without eating.

The flip side (not eating for several days, or not consuming the minimum amount of calories over a long period of time) can lead to malnutrition. This, in turn, messes with your body chemistry, as it slows down and relies on protein and fat as its source of energy rather than carbohydrates. After 48 hours with no food your glycogen stores run out, and your body needs glycogen to power red blood cells and the brain.

Other Reasons Undereating Isn't Healthy

Slower metabolism
With not enough calories to help you get through your day, your body adapts by slowing your metabolism. This can make you feel sluggish and irritable. Moreover, it takes your body time to recover and your metabolism to kick in again once you resume normal eating.

Negative impact on muscles and organs
When you don't eat enough and your body doesn't maintain its minimum blood glucose level, it will break down muscles and organs. Over an extended period of time, the result is weakened and damaged vital organs.

Risk of nutrient deficiencies
Prolonged starvation leads to deficiencies in calcium, iron, zinc, and essential vitamins. In addition, it leads to electrolyte deficiencies and protein malnutrition.

Is Undereating Ever OK?

Some individuals have found benefit in a medically supervised low calorie diet. This involves eating less than 800 calories per day, but uses special shakes, soups and bars to make sure the minimum amount of nutrients are being consumed.

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