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.
“On a day you don't eat for 24 hours, you're guaranteed to be losing a third or half a pound of non-water weight that's mostly from body fat,” Pilon told Global News. “The truth is intermittent fasting is a way to create slow, steady weight loss.”
This phenomenon is called “starvation mode,” and while your body isn't actually starving, it will naturally hold onto whatever calories it receives in an effort to help you maintain your energy balance.
After two or three days without food, your body starts to break down fatty tissue. Your muscles use the fatty acids created during this process as their main source of fuel. Fatty acids are also used to form ketones in the liver. Ketones are another substance the body can use for energy.
However, other studies show that while consuming 1,000 calories a day may result in significant weight loss, most people cannot sustain it and often experience significant weight regain . The reasons include regaining lost muscle mass and increased appetite. Also worth noting is that the human body can adapt.
Would you believe that eating less can result in more belly fat? It's true. While intuitively it makes sense that eating fewer calories will lead to a flat stomach, the reality is that because of the effects undereating can have on certain hormones, not eating enough can lead to fat accumulation on your midsection.
Most people need significantly more than 1,200 calories a day. Therefore, individuals who cut their daily intake to 1,200 calories can expect to lose some weight.
Altogether, it seems possible to survive without food and drink within a time span of 8 to 21 days. If a person is only deprived of food, the survival time may even go up to about two months, although this is influenced by many factors.
For most people, there are no serious dangers involved in eating one meal a day, other than the discomforts of feeling hungry. That said, there are some risks for people with cardiovascular disease or diabetes. Eating one meal a day can increase your blood pressure and cholesterol.
Water fasting will likely result in lean muscle wasting, or muscle mass loss that occurs when you don't take in protein, she says. To compensate, your body starts to break down muscles. You might develop other nutrient deficiencies as well.
If you go long enough without eating, you will use up the glucose in your system and then enter ketosis. During ketosis, your body switches to an alternative fuel source, ketones, which your body makes from fat. If you've ever been to a decent holiday party you've noticed that putting on fat is pretty easy.
People can survive up to three weeks after they stop eating. However, without staying hydrated (without water) as well, the human body can only live 3 to 5 days. Researchers believe that a person can live for up to three weeks without food as long as they have water to drink.
You will not gain weight from eating too few calories.
There are many reasons why it can seem like under-eating can lead to weight gain. But, science has shown over and over again that this isn't physiologically possible.
Too many starchy carbohydrates and bad fats are a recipe for that midsection to expand. Instead, get plenty of veggies, choose lean proteins, and stay away from fats from red meats. Choose healthier fats in things like fish, nuts, and avocados. Even a moderate cutback on carbs (grains, pasta, sugars) can help, too.
Very Low-Calorie Diet (VLCD)
On a VLCD, you may have as few as 800 calories a day and may lose up to 3 to 5 pounds (1.5 to 2 kg) week. Most VLCDs use meal replacements, such as formulas, soups, shakes, and bars instead of regular meals. This helps ensure that you get all of the nutrients you need each day.
If you're a man, woman weighing over 164 pounds or a female who regularly exercises and you aren't losing weight eating 1,200 to 1,500 calories daily, it may be time to see a doctor. Hormone imbalances – such as underactive thyroid – can decrease your body's metabolism and inhibit or prevent weight loss from occurring.
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.
Eating for 12 hours and then fasting for 12 hours is likely safe for most people, Longo explains. “That pattern of eating is very common among people who have record lifespans,” he says.
Some markers include reduction in blood pressure and cholesterol levels, and surprisingly an increase of energy and clarity of thinking. One theory is that hunger initiates a constant stress level that makes us stronger and more resistant to aging.
Many medical experts agree that a one-day fast can feel great. But extending beyond three days can begin to cause harm, especially if you have other medical conditions, such as diabetes or heart disease. “A fast longer than a day or two can deplete vitamins, minerals and electrolytes,” Dr. Hopkins says.