Low-Calorie Diet: How Low Is Too Low?

When it comes to dropping pounds, there’s no denying that calories matter. Eat fewer of them and you’ll see a descending number on the scale.

However, calorie cutting for weight loss requires balance. Our bodies need sufficient calories to function properly, and it's possible to eat too few of them, even when you’re trying to lose weight. Reducing calories too drastically for too long can derail your efforts to slim down, and may cause health problems.

Healthy calorie cutting for weight loss doesn’t mean testing how low you can go. The correct amount will help you lose weight and maintain your well-being.

A low-calorie diet is one that contains fewer calories than you generally consume, says Bonnie Taub-Dix, RDN, the creator of BetterThanDieting.com and the author of Read It Before You Eat It — Taking You From Label to Table, who is based in New York City. General guidelines for weight maintenance suggest a range of 1,600 to 2,400 calories for women and 2,200 to 3,000 for men. So, anything below these numbers is a low-calorie diet.

Overall, eating fewer calories leads to fewer pounds. Eating more has the opposite effect.

But there is a limit to how much you can reduce before you have symptoms of malnutrition. For the best results, speak to a healthcare provider about the best way to cut calories and still have a balanced diet.

Regardless of your mental health history, a super-low-calorie diet may not be sustainable in the long term. We all need calories for survival. If your body senses it’s not getting enough, it will fight the process with a mechanism known as “starvation mode.” “Starvation mode is a defense mechanism that the body uses to prevent fat loss and starvation. The idea is, your body wants to use your fat to keep you alive, so you don’t burn as many calories,” says Felix Spiegel, MD, a bariatric surgeon at Memorial Hermann Medical Group in Houston. “This lowers your metabolic rate, which means you’re using less calories. If you cut back your calories too much, it hinders weight loss.”

To prevent weight loss plateaus, Dr. Spiegel recommends a goal of 1 to 2 pounds lost per week. “If you lose more than that, you’re losing body fluid and muscle mass.”

• Fatigue or low energy
• Constant hunger
• Irritability
• Brain fog or inattention
• Hair loss or brittle hair
• Dizziness
• Anxiety, depression, or mood swings
• Inability to get warm

If you’re looking to trim down by shaving calories, it’s critical to do so safely. Before you start a low-cal diet, consider discussing your plan with a registered dietitian or other healthcare professional who specializes in weight loss. (Bariatric doctors and certified bariatric nurses are other helpful providers.) And before and during your journey, Kalyn True, RDN, who practices in Houston, says to keep a food journal to help you evaluate and reflect on your diet choices. It can also help you determine whether you’re eating enough. Tracking apps like Lose It! or LifeSum are other useful resources for tallying exact numbers of calories per day.

True recommends paying attention to the contents of your plate, for example by following the USDA’s MyPlate guidance for healthy eating. “A balanced plate would consist of half fruits or nonstarchy vegetables, one-quarter of the plate being a plant or animal protein source, one-quarter being a carbohydrate source, and 1 or 2 tablespoons of fat per mealtime.” This way, you can meet your nutrient needs without going overboard on calories.

Finally, remember that slow and steady wins the race. “The healthiest approach is a moderate decrease in daily calories and a moderate increase in daily exercise,” says Spiegel. “Don’t try to lose too much weight at once. Even decreasing your caloric intake by 200 to 300 calories a day and increasing your exercise by 20 minutes a day can go a long way for your long-term success.”

Editor's Note: Lose It! is owned by the Everyday Health Group.

• Following a low-calorie diet means consuming fewer calories than you use.
• Reducing calories can help you lose weight and improve heart health and risk factors for chronic diseases, and may also slow aging.
• Restricting calories too much may be harmful and put your body into starvation mode.
• For the best results, combine a moderate caloric reduction with exercise and monitor your progress with a healthcare professional.