7 Ways Extreme Dieting Messes With Your Body
Fad diets that promise rapid weight loss by severely slashing calories or eliminating entire food groups are tempting. However, these extreme forms of dieting can negatively impact your physical and mental health in numerous ways. Here are 7 of the most concerning effects that crash dieting has on your body.
1. Slows Down Your Metabolism Dramatically
When you cut your calorie intake well below what your body requires, your metabolism immediately starts to slow down. This is because your body thinks it is starving and so it acts to preserve energy and survive (1).
Your basal metabolic rate, which is the minimum number of calories your body burns just carrying out basic functions like breathing, declines significantly. This is known as “adaptive thermogenesis” and it can persist even after you stop the diet (2).
A large 2012 study found that metabolic rate dropped by more than 600 calories per day in men and women who lost 10–20% of their body weight on a weight loss reality TV show (3).
This metabolic slowdown makes it very challenging to continue losing weight. You have to continually restrict more calories just to keep seeing the number on the scale go down.
Crash diets can also cause long-term decreases in the number of calories burned through the thermic effect of food (TEF). TEF refers to the energy your body expends digesting and absorbing nutrients (4). If you restrict overall food intake, your TEF drops.
Furthermore, severely limiting carbohydrates to under 50 g per day, as in a ketogenic diet, reduces TEF compared to a moderate carb intake (5). Less energy is burned digesting and metabolizing food, making weight loss tougher.
In summary, the metabolic slowdown induced by extreme dieting makes weight loss progressively more difficult and frustrating. It also often leads to weight regain when normal eating is resumed.
2. Causes Loss of Lean Muscle Mass
When calorie intake is drastically reduced, along with burning fat your body also breaks down and burns lean muscle mass for fuel (6). The loss of metabolically active muscle further slows your metabolic rate.
Muscle loss also decreases strength and exercise endurance, making it harder to be active and burn additional calories through physical activity.
A major driver of catabolism of muscle on low-calorie diets is inadequate protein intake. Consuming insufficient protein while cutting calories leads to greater loss of lean mass compared to a diet with higher protein (7).
Adequate protein is critical to help preserve your muscle as you lose weight. Shoot for 0.7 to 1 gram of protein per pound of body weight daily. Include lean protein sources like fish, chicken, Greek yogurt and eggs (8).
The scale may still show overall weight going down, but on a crash diet a significant amount of what is lost can be water and lean tissue rather than pure body fat. Losing muscle is counterproductive and makes long-term weight control very difficult.
3. Increases Risk of Nutrient Deficiencies
When you severely restrict or eliminate certain foods or entire food groups, you raise your risk of nutritional deficiencies. Here are some examples:
- Low-carbohydrate, high-protein diets – Often lacking in fiber, vitamin C, magnesium, potassium and other micronutrients concentrated in fruits, starchy veggies, whole grains and legumes (9).
- Low-fat diets – Often insufficient in omega-3 fatty acids, vitamin E, calcium, zinc and more found in foods like olive oil, fish, nuts, seeds and full-fat dairy (10).
- Intermittent fasting – Can make it hard to meet needs for nutrients like calcium, iron, B vitamins, zinc and magnesium if eating window is too small to get daily recommended amounts .
Deficiencies in nutrients can lead to symptoms like fatigue, headaches, muscle cramps, weakened immunity, mood issues, diarrhea or constipation. They also increase disease risk over the long-term.
Make sure to eat a balanced, varied diet with adequate calories to obtain a full spectrum of vitamins and minerals your body requires. Consider a multivitamin as well if restricting foods.
4. Causes Dehydration
Carbohydrates are stored in the body along with water. So when carb intake is drastically cut, as in a low-carb or ketogenic diet, a substantial amount of water weight is lost in the early stages of the diet.
Furthermore, limiting overall food and beverage intake as part of an extreme diet increases risk of dehydration . Without adequate fluids, you may experience issues like:
- Dry mouth
- Headaches
- Dizziness
- Fatigue
- Constipation
- Impaired athletic performance
Make sure to drink sufficient non-caloric fluids like water, seltzer or unsweetened tea or coffee. Get at least 2 liters daily while dieting to stay hydrated. Urine color is one simple way to gauge hydration – light yellow means you are well hydrated.
5. Raises Cortisol Levels
Any kind of crash diet imposes significant physiological stress on the body. As a result, levels of the primary stress hormone cortisol become elevated .
Having chronically high cortisol from restrictive dieting can lead to increased appetite and cravings, especially for high-sugar foods. This makes adhering to the diet a constant battle.
High cortisol levels also promote breakdown of lean muscle tissue . The combination of increased cravings and muscle catabolism makes fat loss progressively more difficult.
Furthermore, elevated cortisol disrupts sleep quality. Poor sleep leads to increased hunger signals and decreased willpower . This vicious cycle makes extreme dieting unsustainable for most people.
6. Causes Physical and Mental Fatigue
When calorie intake is drastically slashed through crash dieting, your body does not have enough readily-available energy from carbohydrates and fats to optimally fuel your cells.
Physical and mental fatigue inevitably sets in. You feel persistently tired, weak and dizzy. Exercise capacity plummets. Even concentration and focus deteriorate as the brain is starved of its preferred energy source, glucose.
Fatigue then triggers more muscle wasting as the body attempts to conserve energy. It also makes it virtually impossible to muster the motivation to exercise and be active – a key component for weight loss and maintenance.
In short, extreme calorie deprivation through crash dieting leads to feelings of burnout, exhaustion and decreased performance across physical and cognitive domains.
7. Compromises Your Immune System
A plethora of studies confirm that restrictive dieting impairs immune function . Combined with nutritional deficiencies, the high stress of crash dieting leaves you more vulnerable to viruses like colds, flu and COVID-19.
Research indicates that very low calorie diets may reduce the activity of certain immune cells like T-lymphocytes and macrophages . Your body diverts its energy toward survival and away from immunity when calories are scarce.
Getting adequate overall calories with sufficient protein is key to keeping your immune system in top working order. Cutting calories moderately while including nutritious whole foods is a more sustainable approach.
In summary, while extreme dieting and very low calorie intakes may result in significant short-term weight loss, they cause concerning ripple effects throughout the body. These include metabolic slowdown, loss of muscle and nutrients, dehydration, high cortisol, fatigue and suppressed immunity.
The Bottom Line
Crash diets that slash daily calories well below recommended levels or completely eliminate entire food groups often backfire. While they may spur quick weight loss at first, the eventual metabolic adaptations combined with nutritional, immune and energy deficits become counterproductive.
A moderate daily calorie reduction of 500-750 calories combined with more movement is the healthiest, most sustainable approach for lasting weight loss and wellness . Be sure to eat a balanced, nutritious whole foods diet with adequate lean protein and stay well hydrated. Working with a registered dietitian knowledgeable about weight management can help optimize your plan.
