You've probably noticed the craze for 800-calorie diets, which claim to help you lose weight rapidly. An 800-calorie meal plan often forms part of a 5:2-style intermittent fasting diet, in which you cut down to 800 calories for a couple of days a week, but eat normally for the other five.
Though fasting has often been thought of as unwise, there's some emerging evidence to support positive health effects from consuming very-low-calorie diets.
Helping With Diabetes
A study in the February 2018 issue of the Lancet found that people with diabetes given an 800-calorie per day liquid diet for three to five months, followed by stepped food introduction and support, lost an average of 10 kilograms (22 pounds) in weight.
More remarkably, nearly half (46 percent) of the patients who started the trial were in remission from diabetes a year later, whereas only 4 percent went into remission in the control group. Almost nine in 10 or 86 percent of those who lost a larger amount of 15 kilograms (33 pounds), had their diabetes go into remission.
However, it's important to note that the people in this trial were being medically supervised. The Mayo Clinic says if you lose weight by crash dieting or by drastically restricting yourself to between 400 to 800 calories a day, you're more likely to regain weight quickly, often within six months after you stop dieting.
Read more: What Will I Lose on an 800-Calorie Diet?
Low-Calorie Dieting Dangers
The Academy of Nutrition and Dietetics says the problems you can run into by consistently eating a low-calorie diet include slowing your metabolism and losing your mental edge (as your brain doesn't have the energy it needs to function properly).
The Academy also says that 800-calorie diets are very likely not to provide enough vitamins, minerals, fiber and phytochemicals for your needs.
According to the National Institute of Diabetes and Digestive and Kidney Diseases, there's a chance that very rapid weight loss can increase the risk of gallstones as well. When you lose weight quickly, your liver releases extra cholesterol into the bile. Fast weight loss may also prevent the gallbladder from emptying properly.
Two Low-Calorie Days
That said, just two low-calorie days a week can be an achievable way to lose weight healthily and effectively. A study published in the October 2013 issue of the British Journal of Nutrition describes a regimen in which women had two low-carb 600-calorie days a week, plus five days during which they consumed an "unrestricted" but healthy Mediterranean-style diet.
The results showed that 65 percent of the two-day dieters successfully lost weight compared with 40 percent of the participants trying to restrict calories a little bit every day. The two-day dieters lost nearly twice as much fat (8.1 pounds compared with 4.4 pounds) in three months, and reduced their risk of breast cancer by achieving greater reductions in insulin resistance than standard dieters.
Read more: How Intermittent Fasting Can Make You Lean
An example of a fasting diet menu for one day (all calorie counts come from the USDA database and add up to 800 calories for one day) might include:
- The Lancet: "Primary Care-Led Weight Management for Remission of Type 2 Diabetes (Direct): An Open-Label, Cluster-Randomised Trial"
- Mayo Clinic: "Which Is Better for Weight Loss — Cutting Calories or Increasing Exercise?"
- Academy of Nutrition and Dietetics: "4 Ways Low-Calorie Diets Can Sabotage Your Health"
- National Institute of Diabetes and Digestive and Kidney Diseases: "Dieting and Gallstones"
- British Journal of Nutrition: "The Effect of Intermittent Energy and Carbohydrate Restriction v. Daily Energy Restriction on Weight Loss and Metabolic Disease Risk Markers in Overweight Women"