Can Eating Too Few Calories Prevent Weight Loss?

You're committed to your diet. You measure your food meticulously and make good choices by choosing lean proteins, whole grains, and fresh fruits and vegetables. You exercise regularly — doing all the "weight-loss" routines, such as high-intensity interval training and strength training. But the pounds refuse to budge. Do you just have a slow metabolism? How is this possible?

You've been taught that reducing your calorie intake is the key to losing weight. But you may be eating too little to lose weight. When you deprive yourself too much, your weight loss stalls and your body holds onto fat. You deny yourself healthy foods unnecessarily, which can have long-term effects on your health.

Human biology makes eating too few calories a bad idea. Understand how many calories is too few, the side effects of not eating enough and how you can re-jump-start your weight loss.

Your metabolism is delicately calibrated to prevent starvation. When you eat too few calories, your body goes into ​preservation mode​. It doesn't know you're trying to fit into a pair of skinny jeans, it just thinks you have no access to food.

A super low-calorie diet, say of 1,000 calories per day or fewer, makes your body sense that it's starving. Appetite hormones kick in to prevent you from losing too much weight. Your metabolism slows, and your body holds onto fat. Any weight you lost initially has made your body smaller too. This means you naturally burn fewer calories at rest.

Your daily metabolic rate can drop significantly as a result of this anti-starvation mechanism, as demonstrated by research published in the journal Obesity in 2016. Researchers followed contestants from the weight-loss reality show ​The Biggest Loser​ for six years following their appearances. The former participants who continued to strive for and maintain weight loss found their metabolisms continued to slow over time, making it harder and harder to lose weight or stay slim.

Eat too little, say just 1,000 calories per day, and your body starts to ​use muscle for fuel​ to spare what it perceives as its best bet at survival: fat. Muscle uses more calories than fat at rest. If you're body is trying to survive, it dumps the most metabolically expensive tissue first.

Research published in Obesity Research and Clinical Practice in 2015 showed that when men with obesity lost a significant amount of weight (14 percent of body mass over 12 weeks), they also lost a lot of muscle mass, particularly in their lower bodies.

As noted, muscle tissue uses more calories than fat at rest and during exercise. If you lose muscle mass, you slow your metabolism further, making weight loss that much harder.

​Read more:​ Good Workouts to Lose Weight Fast

Eating too few calories can also cause your body to pump out fewer of the hormones that make you feel full and more of those that make you feel hungry. The hormone leptin decreases hunger and the hormone ghrelin increases it. When you restrict calories significantly, your levels of leptin plummet and ghrelin increases — this is your body's attempt to ​keep you from starving​.

Because of uncontrollable hunger, it can be hard to stick to a restrictive diet, so you may cheat, binge and undermine your intentions. You crave high-calorie foods and can't stick to your low-calorie plan to lose weight. This isn't a lack of willpower, it's your attempts to eat too few calories that are undoing your valiant efforts to drop pounds.

When you're eating too few calories, you may develop ​nutrient deficiencies​. Healthline points out that you may become deficient in protein, calcium, biotin, thiamine, vitamin A and magnesium.

Nutrient imbalances cause fatigue and low energy, negatively affect bone and muscle development, and compromise the health of your skin, hair and nails. You may find your physical performance suffers, too — especially relevant if you're an athlete.

​Read more:​ Vitamin Deficiency and Thinning Hair in Women

Infertility can also occur as a result of too few calories. Your body's production of sex hormones may reduce because of a too low-calorie intake. The American Journal of Endocrinology, Physiology and Metabolism published a study in 2015 showing that, in women, reductions in calories of 22 to 42 percent below what's needed to maintain their weight can lead to menstrual irregularities indicating problems with ovulation.

You may also find your immune system weakens and you become more ​hangry​ all the time. Mood disorders and depression can occur.

Generally, eating fewer than ​1,200 calories per day for women or 1,500 for men​ is not advised. Harvard Health Publishing explains that this can cause nutritional deficiencies and may trigger a lowered metabolism and hormone imbalances.

You may wonder exactly how many calories you should aim to eat then. Everyone is different, which is why using a weight-loss calculator makes sense. And if you have an existing health issue — such as diabetes — it's important for you to discuss your low-calorie plans with your doctor.

Although you may desire fast results, it's best to stick to losing just 1 to 2 pounds per week. This means cutting only 500 to 1,000 calories out of your diet daily, provided it keeps you above the 1,200 or 1,500 minimum. You may also need to build more physical activity into your day, especially if you're sedentary. Aim for at least 30 minutes of activity most days of the week.

​Read more:​ Recommended Caloric Intake for Weight Loss

When you lose weight, you want to lose fat and keep it off for the long-term. Shortcuts like eating just 1,000 calories per day may cause you to drop weight right away, but you'll only see your losses slow down and often stop. You'll lose lean muscle too, which only hurts you in the long run by lowering your metabolism and endangering your health.

Use a calculator, such as MyPlate, to track your daily calories and make sure you're getting enough nutrients and fuel to power your days, while not overconsuming so as to gain weight or stand in the way of weight loss.