When a person has been eating a low-calorie diet for long enough to actually be starving—there's no specific caloric threshold or length of time for this to happen because it's so individual, the experts explain, but it certainly takes longer than a day without food—a few physiological processes take place.
In other words, if you stick to the calorie intake recommended by WLR, you can be sure your body won't go into starvation mode. As a general rule though, most nutrition experts recommend never going below 1,000-1,200 calories a day if you're dieting on your own.
"[Starvation mode] occurs in people that are severely, severely malnourished and that have burned all their fat away," she explained. "Now they're burning away at the muscle, that tends to be the situation in which it's used."
Consuming at least 1,200 calories per day has often been touted as the minimum for basic bodily functions and to stay out of starvation mode, but the amount is actually too low. A healthy amount of calories for adult women ranges from 1,800 to 2,400 calories per day and for men it's 2,000 to 3,200 calories per day.
No, it is not. The 900-calorie diet plan can be referred to as a very-low-calorie diet. Very low-calorie diets, aka VLCDs, are eating plans that restrict caloric intake to 800 to 900 calories per day. For an adult, such small quantities of food cannot give you enough energy to properly sustain you.
For weight maintenance, the Dietary Guidelines for Americans 2020–2025 suggest a range of 1,600–2,400 calories for women and 2,200–3,000 for men — so you could consider anything below these numbers a low-calorie diet. But some popular diet plans take users to extremely low levels.
Ordinarily, the body responds to reduced energy intake by burning fat reserves and consuming muscle and other tissues. Specifically, the body burns fat after first exhausting the contents of the digestive tract along with glycogen reserves stored in liver cells and after significant protein loss.
Most adults need a minimum of 2000 calories to sustain metabolism, muscle activity, and brain function. However, too many calories can lead to weight gain and a variety of diseases.
Experts tend to recommend eating every three to four hours for optimal energy and health. Starvation mode happens over the long-term, so skipping a meal every once in a while won't permanently affect your metabolism.
If you don't eat enough, your metabolism switches to slow-mo. Severe diets, especially when you also exercise, teach your body to make do with fewer calories. That can backfire, because your body clings to those calories, which makes it harder to take weight off.
If you drastically slash calories and are eating a very low-calorie diet (Think: less than 1,000 calories for women and less than 1,200 calories for men), “starvation mode” can actually be starvation. Starvation from chronic undereating can be counterproductive to weight loss and dangerous to your health.
What happens to the body when it starves. Research indicates people who used starvation diets for weight loss, eating 50% of their energy needs for three weeks, did decrease their body weight overall.
Although some diet plans may recommend consuming 1,000 calories a day or less as an effective tool for weight loss, it is not safe and is an unsustainable way to try and lose weight.
According to the National Institutes of Health, the average adult needs 1,600 to 3,000 calories per day. Although the exact number of calories needed vary based on age and physical activity, 700 is very low. A 2-year-old who engages in minimal physical activities needs at least 1000 calories in a day.
Consumption of under 1,200 calories per day for women and 1,800 calories per day for men can eventually lead to starvation mode symptoms.
For many people, it is safe to eat 1300 calories a day as long as you balance your meals well, and ensure each meal has the required nutrients. In general, people need a minimum of 1200 calories a day, as advised by Everyday health (4).
Myth or Fact: If you cut down on your food intake, you'll eventually shrink your stomach so you won't be as hungry. Answer: Myth.
The body attempts to protect the brain, says Zucker, by shutting down the most metabolically intense functions first, like digestion, resulting in diarrhea. "The brain is relatively protected, but eventually we worry about neuronal death and brain matter loss," she says.
In addition, consuming as few as 800 calories daily may not give you the energy you need for daily living and regular physical activity, especially if you eat the same foods every day. Talk to your doctor or dietitian to make sure you get the nutrients you need while on a very low-calorie diet.
Jesse Feder, Registered Dietitian, says, “ A person can only survive short term on 500 calories a day. This is extremely low and can lead to serious health issues over time.”