After eight hours without eating, your body will begin to use stored fats for energy. Your body will continue to use stored fat to create energy throughout the remainder of your 24-hour fast. Fasts that last longer than 24 hours may lead to your body to start converting stored proteins into energy.
Weight loss isn't the only culprit for a slower metabolism. If you eat too few calories or go too long between meals (more than three or four hours), your metabolism will slow down. This is known as "starvation mode" and is due to the same protective mechanism that happens when you lose weight.
Eating too few calories can cause a major decrease in metabolism. Although a calorie deficit is needed for weight loss, it can be counterproductive for your calorie intake to drop too low.
It Can Lower Your Metabolism
Regularly eating fewer calories than your body needs can cause your metabolism to slow down. Several studies show that low-calorie diets can decrease the number of calories the body burns by as much as 23% ( 8 , 9 , 10 ).
Eating Breakfast Does Not Boost Your Metabolism
It makes no difference at which times, or how often, you eat. Studies show that there is no difference in calories burned over 24 hours between people who eat or skip breakfast ( 8 ).
Skipping breakfast and other meals is one behavior studied as a factor influencing weight outcomes and dietary quality. Based on evidence that skipping breakfast reduces total daily caloric intake, some weight-loss recommendations include skipping breakfast (i.e., intermediate fasting) as one strategy to use.
Factors that may increase a person's metabolic rate include consuming an appropriate number of calories, favoring protein over carbohydrates and fat, getting enough sleep, and some types of exercise, such as resistance training.
Unintentional weight gain occurs when you put on weight without increasing your consumption of food or liquid and without decreasing your activity. This occurs when you're not trying to gain weight. It's often due to fluid retention, abnormal growths, constipation, or pregnancy.
Eating too few calories can be the start of a vicious cycle that causes diet distress. When you cut your calories so low that your metabolism slows and you stop losing weight, you probably will become frustrated that your efforts are not paying off. This can lead you to overeat and ultimately gain weight.
A prolonged 1,200 calorie-per-day diet can slow metabolism, so it is best to only do it short-term. There are risks to consuming too few calories, including: Not getting adequate nutrition. Anxiety.
Intermittent fasting is a convenient way to lose weight without counting calories. Many studies show that it can help you lose weight and belly fat.
Longer periods without food, such as 24, 36, 48 and 72-hour fasting periods, are not necessarily better for you and may be dangerous. Going too long without eating might actually encourage your body to start storing more fat in response to starvation.
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.
Starvation calories are an intake of fewer than 600 calories per day, however; any caloric intake below the recommended minimum doesn't provide the body with the fuel it needs to function properly. A starvation diet doesn't promote weight loss because your metabolism slows down in response to low caloric intake.
Mental health conditions, like anxiety, depression, and stress, can all have a negative effect on hunger levels. Other physical conditions, such as pregnancy, hypothyroidism, and more, can also cause a decrease in appetite.
To achieve weight loss you need to consume less calories than you expend. Eating less can certainly help. However, when people restrict calories too much they often lose lean body mass. A loss of lean body mass is not desired because it weakens the organs and muscles, and also slows down metabolism.
Dehydration causes your body to retain excess water, which can lead to 5 pounds of weight gain overnight (5). When you feel thirsty and drink a lot of fluid at once, you'll absorb the extra fluid quickly and it shows up on the scale within 24 hours.
In some people, especially those who have been dieting or fasting, a meal high in carbohydrates, such as pasta or rice, can be stored as glycogen. Glycogen is stored with water, which causes an individual to gain water weight very quickly – as much as 2 pounds overnight.
Not eating won't directly lead to weight gain -- in fact, you may lose weight as you'll temporarily eat fewer calories than you burn. The problem is that fasting is unsustainable, so any weight-loss benefit will likely be short lived and your health will pay the price.
Water is the key to life, and it turns out it's also one of the easiest ways to help your metabolism. Drinking water increases your metabolism by up to 25% for nearly an hour after drinking it. That means if you drink a few cups of water every hour, you'll keep your metabolism at peak performance all day.
"The biggest thing people do that slows their metabolism down is eating too few calories," said Fiore. 1200 calories per day is roughly the amount you need to perform basic functions, she suggested, and when a person eats fewer than that, the metabolism slows down to conserve energy.
The magic number of calories bandied about for decades has been 3,500—subtract that number from your diet or burn off 3,500 calories more than what you consume, and you'll lose 1 lb.