What makes you eat?


There must be a powerful drive to eat. Who has time for multiple meals every day? How much of my life have I wasted pushing a cart in Kroger? At least I get to say hi to lots of people.

Most of the calories you burn, unless you’re running a marathon or racing in the Tour de France, are burned by your basal metabolism. The basal metabolism goes on all the time even when you are sleeping. Basal metabolism comes mostly from the fat free mass (FFM), or lean body mass – your brain and liver and kidneys and heart etc… – that’s not fat. So this is what makes you eat.

Most people who are not dieting stay the same weight for long periods of time and studies show that how much they eat depends on their lean body mass. (1) This makes sense because that drives the basal metabolism. It has nothing to do with how fat they are except that obese people have more FFM besides having too much fat – they are taller and have bigger hearts and livers and brains… – so that is why they have to eat more. When you lose weight, besides the fat, you also lose lean body mass and this is the driver to eat to recoup. This was demonstrated by data from the famous starvation experiment, The Minnesota Experiment by Ancel Keys, during World War II on conscientious objecter volunteers. After they had regained all their weight and fat stores after the starvation phase, they were still hungry because there remained a FFM deficit. They all wound up a little fatter than before they started. The FFM recuperation lagged behind the fat reaccumulation and kept driving hunger pain.

Your lean body mass has no direct signal to eat. It seems to have all it’s effect indirectly by its influence on basal metabolism. But when you lose fat free mass is that what makes you hungry? Does the decrease in basal metabolism signal the brain or is there some other signal to eat more?

When you lose weight you should need to eat less because your basal metabolism goes down even more than what is accounted for by loss of FFM but there is a counter influence to eat more that is apparently way more powerful. So the brain can’t be watching basal metabolism. That would be telling you to eat less. There must be a different mechanism. Likewise what makes you stop eating when you gain weight? Remember nobody keeps gaining forever.

These questions remain because we have been paying too much attention to signals from fat stores in the body and not enough to the real driver – FFM. But in the meantime maybe you should not be trying to lose weight if it is going to make you fatter later when collateral fat is gained because of the lagging lean body mass gain. Oy.

John DiTraglia M.D. is a Pediatrician in Portsmouth. He can be reached by e-mail- jditrag@zoomnet.net or phone-354-6605.