What Happens When You Stop Eating to Lose Weight?

Maybe you have an event coming up and you need to fit into a dress, ASAP. You figure you'll just stop eating, and that will do the trick. But going without food can have some uncomfortable side effects in the short-term and more serious long-term side effects that can thwart your weight loss goals.

The basic premise of weight loss is to reduce your calorie intake below your calorie expenditure to lose weight, but it's not really that simple. Weight loss and fat loss are two different things, but people often use them interchangeably. Your weight is the number you see on the scale; it includes not only your body fat — the jiggly stuff you want to get rid of — but also your bones, organs and connective tissue, including your blood. You're also carrying around a good deal of water weight.

The goal with healthy weight loss is to burn fat, but preserve as much of your lean body mass as possible — and protect the health of your organs and other tissues. When you cut calories conservatively, your body is able to adjust to the change and keep working as normal. When you cut out most or all of your calories, your body will break down whatever it can find for energy.

Although it can find alternate sources of energy for a short period of time by drawing on lean muscle and fat stores, your body has to work very hard to get the energy it needs. Therefore, the most common side effect of a fasting diet is fatigue — both physical and mental. Your brain requires a steady stream of glucose to operate effectively and, according to the Academy of Nutrition and Dietetics, undereating can cause you to lose your mental edge.

You may also experience constipation, diarrhea and nausea. Just the hunger pangs alone can be very uncomfortable.

And for all that trouble, you're not going to lose much fat on a crash diet — or crash fast. You may see the number on the scale go down, but that's primarily from losing stored carbohydrate, water weight and some lean muscle mass, according to a research article published in the ​Journal of the Academy of Nutrition and Dietetics​ in June 2014. Relatively little of the initial weight loss is fat.

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Your body will start burning fat more quickly after several days or weeks. But you will also still be losing muscle mass. The Academy of Nutrition and Dietetics explains that when you don't eat enough, your body enters starvation mode, in which it breaks down muscle to access stored glucose it can use for energy.

To conserve energy, your body will start slowing or shutting down organ systems and bodily functions. Symptoms that may result from this include:

• Gastrointestinal distress
• Feeling cold all the time
• Depression
• Anxiety
• Fainting
• Loss of menstruation
• Hair loss
• Dental erosion and dental pain
• Dry skin
• Dry, brittle nails
• Hair thinning and hair loss
• Swelling around the salivary glands
• Growth of fine hair on the body
• Poor wound healing
• Frequent infections

Many of the side effects of not eating are due to nutrient deficiencies. Your body needs protein, carbohydrates, fats, vitamins and minerals to function properly. Without these nutrients, your organ systems can't do their jobs.

For example, without enough vitamin B12 and the mineral iron, your body can't make the red blood cells that carry oxygen throughout your body. This results in a condition called anemia that causes symptoms including chronic fatigue, muscle weakness, a smooth and tender tongue and a fast heartbeat.

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Protein deficiency affects all your organ systems, since protein is the building block of all the cells and tissues in your body. Lack of protein results in muscle wasting, increased infections due to poor immune system function, a large belly that sticks out, rash, edema and lethargy or apathy.

Deficiencies in the minerals calcium and vitamin D result in bone density loss. Your bones may become brittle and break easily. Severe vitamin D deficiency can cause a condition known as rickets, in which the bones become soft and bendable. Another condition caused by severe vitamin D deficiency is osteomalacia, which causes weakened bones and muscles and muscle pain.

Low levels of vitamin C cause scurvy, the early signs of which include fatigue, malaise and sore gums. As the deficiency progresses, the body's ability to produce collagen is impaired, weakening connective tissues which causes changes in skin and hair, joint pain, depression, swollen gums that bleed easily and loss of teeth, reports the National Institutes of Health.

Starving yourself in the hopes of losing weight is detrimental to your physical and mental wellbeing. While you may lose fat and appear thinner, the rest of your appearance will suffer when you lose muscle tone, and your skin and hair become dry and brittle.

You can achieve the weight-loss results you want, and feel and look healthy while doing it, by eating a balanced, calorie-sufficient diet that provides all the nutrients you need. Cutting out processed foods that are high in calories and low in nutrients, and replacing them with fresh, whole foods that are nutrient-dense will help you create enough of a calorie deficit to shed fat.

Eating enough protein will help you maintain muscle mass as you lose weight, and complex carbohydrates from fruits, vegetables and whole grains will give you the energy to exercise regularly to burn calories and build muscle.