The Science of "Starvation Mode"

The Science of "Starvation Mode"

I am not promoting any diet or particular intake level. The reason for this post is to encourage MFP members to learn more about the science behind "starvation mode". For those of you that like science I suggest reading some scientific studies on the topic. Wikipedia contains a lot of helpful citations:

http://en.wikipedia.org/wiki/Starvation_response

From Wikipedia:
"Starvation response in animals is a set of adaptive biochemical and physiological changes that reduce metabolism in response to a lack of food."

This basically means that after a certain point metabolism can slow down. Metabolism never stops as long as we are alive. The relevant question is how much metabolism slows.

From Wikipedia:
"Starvation mode is a state in which the body is responding to prolonged periods of low energy intake levels. During short periods of energy abstinence, the human body will burn primarily free fatty acids from body fat stores. After prolonged periods of starvation the body has depleted its body fat and begins to burn lean tissue and muscle as a fuel source."

Naturally, a morbidly obese person has an abundant supply of fat stores to begin with and can go a much longer period of time before burning significant lean muscle tissue for fuel (the same reason why a fat bear can hibernate for a much longer period than a bear who was lean before winter began). For this reason, scientific studies of long term very low calorie diets are ONLY conducted on overweight individuals. If someone is very lean to begin with they are at a much greater risk of losing lean muscle mass while eating under TDEE. For centuries before food became so easily available we had periods of feast and famine. During the famine period most people ate very low calorie diets. Some of them died. Who was more likely to survive? Naturally the people who were very overweight before the famine began (unlike today, for much of history it was the rich population who was obese, often by choice for this very reason). People who were very lean before the famine began often did not do well. This is the same reason very low calorie diets should not be used over the long term by underweight people today.

Remember, starvation mode relates not to metabolism stopping completely, but the "adaptive biochemical and physiological changes that reduce metabolism in response to a lack of food." Anyone who eats at a deficit to TDEE will lose weight over time. If you believe this is not the case for you, then you are either incorrectly measuring your intake or incorrectly calculating your TDEE. Any other explanation defies science. The magnitude and speed of the metabolic slowdown will depend on the individual.

Again from Wikipedia:
"The magnitude and composition of the starvation response (i.e. metabolic adaptation) was estimated in a study of 8 individuals living in isolation in Biosphere 2 for two years. During their isolation, they gradually lost an average of 15% (range: 9–24%) of their body weight due to harsh conditions. On emerging from isolation, the eight isolated individuals were compared with a 152-person control group that initially had had similar physical characteristics. On average, the starvation response of the individuals after isolation was a 180 kcal reduction in daily total energy expenditure. 60 kcal of the starvation response was explained by a reduction in fat-free mass and fat mass. An additional 65 kcal was explained by a reduction in fidgeting, and the remaining 55 kcal was statistically insignificant."

My only goal is to help more MFP members understand what "starvation mode" actually means as I believe it is among the most misunderstood terms in the forums. I am not advocating that anyone start a very low calorie diet. Just because "starvation mode" is misunderstood as applied to many people, does not mean I think a very low calorie diet is the best method for anyone. Each individual should make his/her own diet decisions with consultation with his/her doctor.

Long term very low calorie diets are NOT appropriate for anyone within either the normal or underweight ranges of the BMI tables. Nor are they appropriate for anyone with medical conditions unless under the care of a medical doctor. However please do not automatically that everyone who consumes under a certain number of calories will automatically enter "starvation mode" and immediately suffer a dramatic drop in metabolism even if they started out as very obese (meaning they have an abundant supply of energy stores). According to the studies cited by Wikipedia metabolism does not stop or even slow down in an overly dramatic fashion for individuals who are severely obese (again this would be a major concern for those who are lean to begin with).

If you want to see more examples, read Table 1 (test of carbohydrate metabolism) in this study of a 382 day fast of an otherwise healthy 27 year old morbidly obese male under medical supervision:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2495396/pdf/postmedj00315-0056.pdf

The good news is that better understanding can help you protect lean muscle mass as you diet. If you are already lean to begin with, huge calorie deficits are more likely to cause muscle loss.

For anyone who wants to lose weight, according to Wikipedia:
"Resistance training (such as weight lifting) can also prevent the loss of muscle mass while a person is energy-restricted."

For those of you that hope to learn more about the true definition of "starvation mode", I hope this post and citations will help clear up some common misunderstandings.