How Starvation or Severe Calorie Reduction Prevents Weight Loss

Graphic abstractHave you ever known someone who eats so little and yet they cannot seem to lose weight?  Perhaps you’ve tried this yourself and been frustrated with the lack of weight loss, despite what seemed like a very low calorie diet. I recall growing up, our family had a friend (lady) who faithfully ate 800 calories a day and was overweight bordering on obese in her 30’s.  I also recall seeing MRI’s of the thighs of a woman who had eaten very low calories for over a decade and it showed almost no muscle, and just bone and fat.

There are a few variables that figure into weight loss.

  1. Your basal metabolic rate, which is how many calories you burn without moving- while sitting or sleeping. You want this high to burn calories and build muscle.
  2. How much you eat. It also matters what you eat, as the low glycemic index foods can trigger ketosis and fat burn. You do need to eat enough, just not too much
  3. How much you exercise. Avoid excess exercise where you are breaking down tissue. Generally more is better for weight loss.

I had always equated the basal metabolic rate (BMR) to one’s gender, and weight, but really it’s based more on these factors:

  1.  Muscle Mass- muscles burn more calories than fat even at rest so the more muscle you have, the more calories you burn, even while sleeping.
  2.  Prolonged fasting or starvation will reduce thermogenesis (the production of heat) and lower your BMR (you burn less calories).
  3.  Prolonged exposure to cold environments also lowers your BMR to conserve energy.

For those who need to lose weight, the study “O-GIcNAc Transferase enables AgRP neurons to suppress browning of white fat,” published in October 2014 in the journal Cell, provides the mechanism by which fasting/starvation or extreme prolonged exposure to cold will cause your white fat cells to “brown” and reduce the heat output of your cells. In addition, you develop insulin resistance and thus you burn fewer calories (lower BMR) and you store more fat. (You can read the article here… )

It was previously known that white fat, which stores excess energy as triglycerides, was energy storing and brown fat promoted more heat production and the use of energy. When our calorie intake exceeds our energy need we typically store energy as fat (triglycerides in the white fat).  While it had been known that white fat could transform to the energy burning brown fat in a process called “browning”, the mechanism had not been determined.  This study shows specifically how this happens.  Prolonged fasting:

  1. Activates the AgRP neurons in the hypothalamus of our brains.
  2. The enzyme OGT (O-GIcNAc transferase) is increased and with
  3. Increased O-GlcNAc (O-linked beta-N-acetylglucosamine)
  4. Suppressing browning of white fat cells.

If you are trapped in the desert with no food, or in the cold wilderness with no jacket, this could save your life.  For most of us, who struggle with our weight, the last thing we want to do is stop the browning of fat cells. We want to burn more calories, and thus we need to take in enough calories to avoid activating this process.

 

 

Dr. Paul

 

 

 

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