Is fasting good for weight loss
The fasting that produces ketosis also causes loss of appetite. Researchers have theorized that having no appetite is an advantage to a person without access to food because the search for food would be a waste of energy. When the person finds food and eats carbohydrate again, the body shifts out of ketosis, the hunger center gets the message that food is again available, and the appetite returns. This chain of events has served as justification for weight loss routines that induce ketosis, such as fasting and fad diets. However, any kind of food restriction, with or without ketosis, leads a person to adapt by losing appetite. A well balanced low-kcalorie diet can induce the same effect. Therefore ketosis-producing diets offer no special advantage to the dieter in terms of appetite suppression, and because ketosis can disrupt the body's acid base balance, other weight loss ways or the use of fat burners are preferred over ketogenic diets.
Slowing of metabolism
In any case, while the body is shifting to the use of ketone bodies, it simultaneously reduces its energy output and conserves both its fat and lean tissue. As the lean (protein containing) organ tissues shrink in mass, they perform less metabolic work, reducing energy expenditures. As the muscles waste, they can do less work and so demand less energy, reducing expenditures further. The hormones of fasting slow metabolism even further in the effort to conserve lean body mass for as long as possible. Because of the slowed metabolism, the loss of fat falls to a bare minimum - less, in fact, than the fat that would be lost on a low-kcalorie diet. Thus, although weight loss during fasting may be quite dramatic, fat loss may be less than when at least some food is supplied.
Symptoms of starvation
The adaptations just described - slowing of energy output and reduction in fat loss - occur in the starving child, the hungry homeless adult, the fasting religious person, and the malnourished hospital client. Such adaptations help to prolong their lives and explain the physical symptoms of energy deprivation: wasting, slowed metabolism, lowered body temperature, and reduced resistance to disease. The body's adaptations to fasting are sufficient to maintain life for a long period. Mental alertness need not be diminished, and even physical energy may remain unimpaired for a surprisingly long time. Still, fasting presents hazards. The same alterations in metabolism occur in low-carbohydrate dieting, as the next section describes.
The low-carbohydrate diet
An economy similar to that of fasting prevails in the person who consumes a low-carbohydrate diet. Once the body's available glycogen reserves are spent, the only significant remaining source of glucose is protein. The low-carbohydrate diet usually provides some protein from food, but some is still taken from body tissue. The onset of ketosis signals that this wasting process has begun. People are attracted to the low-carbohydrate diet because it brings a dramatic weight loss within the first few days. They would be disillusioned if they realized that much of this weight loss is a loss of glycogen and protein together with large quantities of water and important minerals. A dieter who boasts of losing 7 pounds in two days on a low-carbohydrate diet must be unaware that at best, a pound or two is fat, and 5 or 6 pounds are lean tissue, water, and minerals. Once the dieter begins to eat a balanced diet, the body will avidly devour and retain these needed materials, and the weight will zoom back, quite often to higher than the starting point. These facts offer a warning: beware of quick weight loss schemes. Learn to distinguish between loss of fat and loss of weight.
The protein-sparing fast
A variant on fasting is the technique of ingesting only protein. The hope is that the protein will spare lean tissue and that the person will break down body fat at a maximal rate to meet other energy needs. The protein does spare the lean tissues to some extent from being used to provide glucose, but the protein also is largely used as a glucose source itself, just as dietary carbohydrate would be. Protein formulas (liquid and powdered) were popular weight loss regimens during the late 1970s - until serious health effects, including deaths, emerged. Since then products have been reformulated to contain high-quality protein, carbohydrates, some fat, vitamins, and minerals. In addition, such formulas are sold only to doctors or hospitals for supervised use and must carry a "Protein Diet Warning" on their labels. Even with more complete formulas, such weight loss regimens present serious health risks and need to be carefully monitored. In addition to the health risks, protein fasts have a low long-term success rate; most people regain the lost weight. Thus the protein-sparing fast has to be judged at best a moderate success and at worst a failure. The term protein sparing has been used in another situation. Hospital clients enduring severe physical stresses such as wasting diseases or major surgery also lose body protein. This is especially likely, and especially dangerous, if they are simultaneously fighting infection, which prevents the body from going into ketosis. Physicians make every effort to prevent the loss of vital lean tissue by supplying amino acids as well as glucose in some form - through a vein if the client can't eat. The effort to provide protein-sparing therapy for prevention of malnutrition should not be confused with the profiteering of faddists who promote the protein-sparing fast for weight loss.