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Do Low-Calorie Diets Lower Metabolism?

If You Make This Mistake When Going Low-Cal, Your Metabolism Will Pay For It

When it comes to losing weight, a lot of weight-loss programs and diets require eating in a calorie deficit. While experts and research support this, it's important that you don't cut your calories too much, as that can be extremely detrimental to your ability to lose weight.

To find out if low-calorie diets are doing more harm than good and messing with your metabolism, POPSUGAR spoke to Avigdor Arad, PhD, RDN, CDE, director of the Mount Sinai PhysioLab.

What Is Metabolism?

Metabolism is an extremely complex process that relates to how your body processes energy from fat, protein, and sugar/carbohydrates and how it stores that energy. Usually, when people talk about their metabolism, they actually mean their metabolic rate, which is the amount of energy, more commonly referred to as calories, you burn in a day. There are a lot of things that can affect your metabolism, such as your age, your hormones, and your diet.

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Why Low-Calorie Diets Slow Down Your Metabolism

"When you eat a very low-calorie diet, 500 or 800 calories a day, it certainly signals [to] your body that there's some food shortage/nutrient deprivation," Dr. Arad told POPSUGAR. "The only way your body can handle it is by conserving energy. Your body is going to slow down your metabolism, for a lack of better terms," he continued. As your body goes into conservation mode, you'll be burning fewer calories.

"It's very difficult to maintain a low-calorie diet, and also, it's very difficult to take in a sufficient amount of nutrients to keep you healthy," he said. "In the long run, what those diets show is that it's not very sustainable and it can affect people's mood and function, and it's just not worth it." Low-calorie diets can slow down your metabolism, and ultimately, "The bang for your buck is not very big," said Dr. Arad.

How Many Calories You Should Eat Per Day

Although extremely low-calorie diets aren't doing your body any good, according to Dr. Arad, calorie-restriction, such as intermittent fasting when done wisely and not too low, "could be extremely helpful." This is because, in his opinion, people are eating more than what their body needs, and that excess energy has the potential to be stored as fat. More importantly, Dr. Arad said to place emphasis on the quality along with the quantity of the calories you ingest.

Like most things in fitness, it's impossible to provide an exact amount of calories you need to consume in a day to function at your best. This is because we all have different resting metabolic rates (RMR) — the minimum number of calories you need in a day for essential bodily functions like breathing and to keep your brain functioning. The most accurate way to determine your resting metabolic rate is to get a specialized RMR test done at clinics such as Fitnescity ($250, but prices may vary). Another way to determine your RMR is by using this formula, but the results will be less accurate.

On average, the USDA recommends that adult women consume between 1,600 and 2,400 calories a day and adult males consume between 2,000 and 3,000 calories a day. These numbers will vary depending on your goals and lifestyle, and if you'd like to find out the optimal amount of calories you need in a day, we advise consulting your doctor, a registered dietitian, or a certified nutrition coach.

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