The consequences of low calorie dieting are automatic and unavoidable. The responses are metabolic, hormonal, and psychological in nature, and include: Decreased metabolism, loss of muscle, increased activity of fat-storing enzymes and hormones, decreased activity of fat-burning enzymes and hormones, decreased thyroid output, increased appetite, increased chance of regaining weight, and decreased energy and work capacity.
1. Very low calorie diets slow down your metabolic rate
The first thing that occurs during a severe calorie shortage is a decrease in your metabolic rate. The lower your calories, the slower your metabolism becomes.
Simply put; when you eat less, your body burns less. When you eat more, your body burns more.
This metabolic slowdown is well researched. When calories are restricted, your metabolism decreases by at least 20-30%. With severe calorie restriction, some studies have shown that resting metabolism can become decrease by as much as 45%! That’s the equivalent of having your daily energy expenditure drop from 3000 calories per day to only 1650 calories per day! This is why, after prolonged low calorie dieting, you can eat very little food and still not lose weight.
2. Very low calorie diets make you lose muscle
The most devastating effect of the low calorie diet is the loss of muscle tissue. Once the starvation alarm is triggered, your body begins looking for ways to conserve energy. Muscle is metabolically active tissue. Getting rid of it is the body’s way of decreasing energy expenditure. It’s easy for your body to use muscle for energy. This process is known Gluconeogenesis – converting muscle into glucose. This includes skeletal muscles, and internal organs, even your heart muscle!
Study after study has shown that very low calorie diets without exercise will always cause 40 - 50% of the weight loss to come from lean tissue. Many diets, especially those that are low in carbohydrates, cause large losses in water weight. Between the loss of water, glycogen and muscle, fully 75% of the weight you lose on such plans is not fat! The initial weight loss on most diets is very deceiving, giving you only the illusion of success. Even with exercise, if a diet is too restrictive, much of the weight loss will still be lean tissue.
3. Very low calorie diets increase activity of fat-storing enzymes and decrease the activity of fat burning enzymes
The main fat storing enzyme is called Lipoprotein Lipase (LPL). When you drop your calories too low, your body will produce more LPL and less fat burning enzymes. In other words, when you don’t eat enough, your body changes its chemistry to make it easier to store fat in the future.
4. Very low calorie diets decrease output of thyroid hormone.
The Thyroid gland is largely responsible for the regulation of your basal metabolic rate (the rate at which you burn calories at rest). When your body senses a severe reduction in calories, there is a corresponding reduction in the output of active thyroid
hormone (T3). The result is a decrease in your metabolic rate and fewer calories burned.
5. Very Low calorie dieting increases the chance of rebound weight gain
Almost everyone loses weight initially on a very low calorie diet, but it never takes long before the body catches on and starts conserving energy. That’s when you hit a plateau. Once you hit the plateau, it becomes much harder to keep losing weight even if your calories are extremely low.
This lack of continued results, combined with gnawing hunger pangs and insatiable craving, usually causes people to give up out of sheer frustration. They go off their diet, the weight creeps back on and their body fat ends up back where they started - only now they have less muscle and a slower metabolism.
With a slower metabolism, what used to be you maintenance level now becomes a calorie surplus, and the weight comes right back on.
Most people gain back all the weight they lost– and some gain back even more, leaving them fatter than when they started. This up and down pattern of weight loss and weight re-gain is commonly known as the “yo-yo cycle”, and it often continues for years or even for an entire lifetime. With each repeated bout of dieting, your metabolism becomes less and less efficient and you can actually become progressively fatter while eating less food.
6. Very low calorie diets increase appetite and cravings.
When your body goes into starvation mode, this triggers increased appetite and cravings in an attempt to get you to eat more food. The hunger and cravings can be so strong that you become ravenous. It’s virtually impossible stay on a diet when you are ridiculously hungry and all you can think about is food. Not many people have that much willpower.
7. Very low calorie diets decrease your energy and work capacity
Low calorie diets leave you tired, lethargic and unable to sustain high levels of activity or intense workouts.
The first sign of under nutrition is the loss of energy and the inability to sustain prolonged physical work. There is a direct relationship between calories consumed and the physical work a person can do.
If you have no energy to work out, you’re going to feel lousy and seriously compromise your results. The ability to train hard aerobically and with weights is critical for your long-term success at fat loss.