Most health care professionals recommend you eat regularly throughout the day when you're trying to lose weight. But you may wonder if you'll have better success at losing weight if you only eat once a day. Though eating fewer meals may help you eat fewer calories, fasting all day can make you ravenously hungry and make it hard for you to eat right. As a result, it may not be the most effective way to lose weight. However, if you're intent on limiting yourself to one meal a day, intermittent fasting -- limiting your calorie intake one or two days a week -- may be a better way to go. Before limiting yourself to one meal a day, consult your doctor to make sure it's a safe eating pattern for you.
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Weight Loss Is About Calories
No matter if you're eating one meal, three meals or six meals a day, whether you lose weight or not comes down to your total calorie intake. When your goal is weight loss, you need to consume fewer calories than you need, which causes your body to burn fat for fuel. To lose 1 pound of fat, you need to consume 3,500 fewer calories, so cutting back by 500 calories a day means you'll lose a pound a week.
Use an online calorie calculator to help you determine your calorie needs for weight maintenance, then subtract 500. For example, a man who is 5 feet 10 inches tall, weighs 200 pounds and rarely exercises needs 2,700 calories to maintain his weight, so he can lose 1 pound a week by limiting his daily intake to 2,200 calories a day.
Calories With One Meal a Day
Eating one meal a day can help you limit your calorie intake, whether you're counting calories or not. While weight-loss calories vary, usually ranging from 1,200 to 1,800 calories a day, you might have a hard time eating all those calories in one meal. If you can lose weight on a higher number of calories, though, it could be even more difficult -- and not very sensible -- to eat them all at one sitting.
Eating fewer than the lower limits -- 1,200 calories for women and 1,800 for men -- may cause you to lose weight faster, but it puts you at risk for nutrient deficiencies, especially if you follow this eating pattern over the long haul. Dropping weight too fast usually results in loss of muscle and water, in addition to fat. Losing muscle may cause a decrease in energy levels and increase your risk of regaining the weight later. And eating too few calories may slow your metabolism, making it harder for you to drop weight.
One Meal a Day vs. Three Meals a Day
While you might be able to limit calorie intake eating only one meal a day, you may be better off eating more often when trying to lose weight, according to a 2012 study published in the Journal of Circadian Rhythms. This study compared the effects of eating one large meal a day -- at breakfast -- compared to eating a bigger breakfast and a small dinner on weight loss in mice fed a high-fat diet. This study found that the mice had an easier time maintaining their weight and had less fat accumulation when they ate two meals a day instead of one.
Although the evidence is less clear in people, it does seem as though eating more often improves weight loss and retention of muscle mass, according to 2015 review published in Nutrition Reviews. While 15 studies were included in this review, the authors note most of the positive data came from one study, so more research may be necessary to confirm that eating more often is beneficial for weight loss.
It May Work Intermittently
Instead of eating only one meal a day all the time, you might be able to lose weight without compromising your health by eating one meal a day only once or twice a week. Referred to as intermittent fasting, or IF, this method allows you to eat freely five days a week and restricts your intake to 500 to 600 calories the other two days, which should be nonconsecutive. So, for example, one way to do IF would be to eat just one 600-calorie meal every Tuesday -- or every Tuesday and Friday.
This eating pattern may be as effective at helping people lose weight as reduced-calorie diets, according to a 2011 review study published in Obesity Reviews, and it may also be better at preventing muscle loss. While there is some good evidence that intermittent fasting is helpful to those trying to lose weight, however, more research is needed to assess safety, especially for those with medical conditions. If this sounds like a diet you might want to try, consult your doctor first.
Concerns About Eating Only One Meal a Day
Eating only once a day means you're fasting for most of your waking hours. Fasting can have unpleasant side effects, including fatigue, constipation and headaches. Also, going several hours without eating may increase hunger levels and lead to poor food choices when you finally do sit down to eat. And while you may not be eating much food throughout the day, you need to drink plenty of water to stay hydrated.
It's also difficult to keep this diet going over the long term. This is not only because it's hard to fast all day, every day, but it may also put a damper on family time and your social life, which often revolves around eating.
If you have diabetes and are taking insulin, you shouldn't go several hours without eating. Also, pregnant and nursing women, teens and children shouldn't follow a diet that limits their intake to one meal a day due to their increased nutrient and calorie needs. If you have a medical condition, such as heart disease or kidney disease, talk to your doctor first before making any changes to your usual diet.