The one-meal-a-day weight loss plan promotes fast weight loss through restricting the time of day during which you eat and the number of meals you eat in a day. This type of diet has different forms, such as intermittent fasting, alternate-day fasting, or eating only one meal a day. It may also be referred to as caloric restriction. The idea is to reduce calories but keep the same nutritional content that your body needs.

This diet works under the concept that restricting your calories to one feeding time ensures that your body stays in a constant state of burning fat. When you eat regular meals and snacks, your body uses those calories at a steady rate for energy. When you take away that steady stream of calories, your body is forced to use fuel from other places, like fat in your body.

Read on to learn more about the health benefits and risks of this type of diet.

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The theory behind the one-meal-a-day diet is that you only eat one meal per day. Most people choose dinner, so they fast all day long and consume all of their calories for that day within that one meal. Your one meal can contain up to the number of calories you need per day depending on your activity levels, and have a healthy balance of carbohydrates, proteins, and fat.

You don’t count calories or focus on macronutrients. Instead, you eat enough to feel full and focus on including foods from all of the food groups.

In some cases, you’re allowed to eat one or two small snacks during the day in addition to your one meal, such as a piece of fruit or a high-protein food, like a hard-boiled egg, after a workout. You’re also allowed liquid no-calorie beverages, such as water, coffee, and tea.

There are few long-term studies on fasting in humans, and many of the studies that have been done focus primarily on fasting in men. Women may be affected by different body processes, such as menstrual cycles, pregnancy, and breastfeeding.

Some studies that have been done on fasting have shown some promising benefits. For example, restricting calories by 20 to 25 percent on a daily basis has been linked to heart health and more stable blood sugar by decreasing glucose levels and increasing how well insulin works. A 2017 study on diabetes found that intermittent fasting for six weeks significantly improved fasting blood sugar levels, as well as body weight in type 2 diabetics. Longer studies are needed to confirm these benefits can be maintained long term.

A two-year follow-up study comparing intermittent fasting to daily calorie restriction reported that intermittent fasting can be a helpful treatment approach for those with prediabetes or insulin resistance.

Restricted eating has also been shown to help with memory in older individuals and may even help increase life span by reducing the processes that can cause disease.

People following the one-meal-a-day lifestyle claim that it can help increase energy, avoid the “afternoon slump,” and keep you full longer.

Intermittent, alternate-day, and other forms of fasting diets can lead to negative side effects such as:

  • extreme feelings of hunger
  • shakiness
  • fatigue
  • brain fog
  • feelings of weakness
  • inability to concentrate
  • binge eating

Fasting can also be very dangerous if you have any medical conditions, such as diabetes or hypoglycemia. Some people may be able to adjust quickly to only eating one meal a day, while others may have difficulty going that long without calories. Everyone is different.

Also, although your body may adjust and not feel hungry when you fast, once you stop, your body may overcompensate by making you feel hungrier. It appears in women who aren’t obese and aren’t yet menopausal that fasting may be more detrimental than beneficial to metabolism and body weight maintenance than for other women or men.

One study on alternate-day fasting revealed that this type of dieting led to the highest dropout rates and increased low-density lipoprotein cholesterol (or “bad” cholesterol) after 12 months. Alternate-day fasting also didn’t lead to more weight loss than daily calorie restriction.

Aside from the physical side effects, there’s also the potential emotional side effects of fasting. It may make you irritable, and this way of eating could lead to binge eating or put you at risk for another eating disorder.

In the long run, fad diets and extreme measures of losing weight aren’t sustainable and can be harmful. There may be some health benefits to intermittent fasting, but there are also some serious risks to using severe calorie restriction as the only way to lose weight. Fasting for extended periods of time, or regularly, may slow down your metabolism, lead to binge eating, and interfere with your efforts to lose weight and maintain the weight loss, though studies are limited on this side effect.

Instead of relying on any single method to lose weight, you should talk with your doctor about safe and effective ways to maintain a healthy weight.

  • Schedule a physical checkup with your doctor. Sometimes weight gain or the inability to lose weight can be linked to an underlying medical condition.
  • Track your food. This tactic has been associated with healthier weights and may help you become more aware of the food and beverages you’re consuming.
  • Educate yourself on nutrition. Your local health center or hospital may have dietitians who offer classes on healthy eating and portion control.
  • Consider buying a food scale so you can weigh and measure your food to learn correct portions.
  • Start an exercise program. It doesn’t matter what you do, just get moving!
  • Join a support group. Meeting with a group of like-minded people, whether in an official weight control program, online, or in your community, is a great way to get support as you get healthy together.

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It’s always a good idea to discuss any diet changes with your doctor, especially if you’re considering a diet with intermittent fasting or severe calorie restrictions. These diets may be harmful for some people.

To maintain weight in the long term, develop healthy, sustainable eating habits, and include regular exercise in your daily routine.

Learn more: Safe ways to lose weight fast »

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