We are making progress in our research and conversations of the disease of overweight/obesity, but there are still huge, gaping holes and I think the role of the hypothalamus fills one of them. Let’s talk hypothalamus today!
The hypothalamus is an area of the brain that controls hormones to maintain homeostasis, or equilibrium. It is here where there is a system to move most physiologic parameters in whichever direction is needed to keep them within the normal range, such as temperature, heart rate, and, you guessed it, body weight. For example, the hypothalamus can raise or lower body temperature, raise or lower thyroid hormone level, and raise or lower body weight. Let’s look more closely at how the hypothalamus regulates body weight so we can see how it may go awry and what we may be able to do about it.
Hypothalamic Regulation of Energy Homeostasis
The hypothalamus is in charge of regulating energy input and output for the purpose of maintaining a body weight or body fat set point. It does this in a few ways:
Resting metabolic rate: this is the metabolic rate at rest. This goes up if your body weight is lower than your hypothalamus thinks you should be, and it does down if your body weight (or body fat stores) are lower than your hypothalamus thinks they should be. This is a large part of metabolic adaptation to weight loss which shows metabolic rates are lower for a given body weight after weight loss. For example, a person who naturally weighs 180 pounds with a 25% body fat will have a higher resting metabolic rate than someone who naturally weighs 230 pounds and lost 50 pounds through diet and exercise and ended up with the exact same 180 pound body weight with a 25% body weight. This is because the person who lost 50 pounds has a hypothalamus that “thinks” 230 pounds and a body fat that is likely closer to 35% is “normal” for that person. Conversely, if a person gains weight, the resting metabolic rate will increase until the weight returns to “normal” also.
Hunger & Cravings: the hypothalamus also drives a person to a weight set point by increasing or decreasing hunger and cravings. There are 2 sets of hormones: orexigenic hormones which increase hunger and the drive to eat, and anorexigenic hormones which decrease hunger and the drive to eat. When body fat and body weight are lower than a weight set point, as happens after weight loss, orexigenic hormones increase and hunger and cravings are increased. This is happening at the same time that the resting metabolic rate has slowed. Other things that increase orexigenic hormones are sleep deprivation and stress. Eating a meal decreases orexigenic and increase anorexigenic hormones. This is why eating at regular intervals can reduce hunger and cravings.