Starvation mode is a metabolic slowdown that occurs when the body receives too few calories for an extended period. The Minnesota study found that a calorie deficit must be severe and long-term to trigger this mode, which can cause weight loss at a slower rate and general torpor. Leptin levels play a role in the physiological mechanism leading to starvation mode. However, weight loss continues in most cases, albeit at a slower rate, and people in starvation mode may experience a severe lack of energy.
Starvation mode refers to a slowdown in metabolism that can occur when the body receives too few calories daily for an extended period of time. The modern theory of metabolic starvation mode is believed to be based almost entirely on a scientific study often referred to as the Minnesota study. This study, conducted in 1950 by researcher Ancel Keys, documented the effects of a starvation diet on a group of healthy young men of normal weight over a period of six months. The study concluded that when daily calorie intake is reduced to at least half of the normal requirement, the basal metabolic rate may decrease. In general, people operating in starvation mode can be expected to continue to lose weight, but they will do so at a slightly slower rate than someone with a normally functioning metabolism, and are expected to experience general torpor.
Concerns about hampering one’s weight loss progress by eating too few calories daily and going into starvation mode can be common among dieters. Keys’ research appears to have established that daily caloric deficits must be severe and extended over the long term to trigger the physiological changes that cause the metabolic slowdown known as starvation mode. Experts believe that this mode has a biological purpose, as it allows the human body to survive during periods of famine, even when body fat stores are small. Keys’ study seems to suggest that starvation mode does not typically begin until the individual reaches a total body fat percentage of less than 6 percent for a woman or less than 5 percent for a man.
The physiological mechanism leading to starvation mode is believed to depend on the action of a hormone known as leptin. Fat cells in the body normally secrete leptin. Blood leptin levels generally help the brain keep track of the extent of physical fat stores. Lower calorie intake and increased weight loss can lower leptin levels, by reducing the number of leptin-secreting fat cells in the body. When the percentage of body fat falls below the minimum necessary level, the reduced leptin levels signal the brain to begin the process of metabolic slowdown.
Starvation mode does not normally prevent further weight loss. Weight loss continues in most cases, although it usually occurs at a slower rate than would be expected in a person who is not in this state. People in starvation mode can also experience a severe lack of energy, as they are unlikely to receive the calories they need to perform normal daily activities.
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