How to Boost my Metabolism: Examining the Set-Point Hypothesis
We all know that our body weight is determined by the amount of calories we consume compared to the amount our body expends for metabolic function and physical activity. So, why is it that two people of the same gender, age, and activity level can eat vastly different amounts of food and weigh about the same?
The Set-Point Hypothesis
A large part of the answer has to do with our set-point. Richard Keesey defined this concept as our body's thermostat that continuously adjusts our metabolism and eating to maintain our weight within a genetically determined range, or set-point.
Since the release of this hypothesis, many researchers have tried to prove or disprove the concept, but biological studies continuously prove the hypothesis to be correct.
For instance, voluntary semi-starvation and over-eating studies have produced the same results: Initially, when we reduce or increase our caloric intake, the change in weight is rapid. But, as the dieting or over-eating continues, the weight loss or gain slows, since our body adjusts our metabolic rate, attempting to maintain our set-point.
Our Basal Metabolic Rate (BMR) is the number of calories our body needs to maintain basic functions while at rest. Our BMR is affected by six factors that contribute to our set-point:
- Heredity: Some people have a naturally higher metabolic rate than others, even when they're sleeping.
- Stress: Stress can raise our BMR by flooding our bloodstream with norepinephrine and epinephrine. However, our body also releases Cortisol, which can lead to increases in belly fat and related illnesses. See: How Does Stress Affect Your Health?
- Age and Activity Level: Younger people generally have higher BMRs than older people who are more sedentary.
- Fat vs Muscle: Fat tissue has a lower metabolic rate (burns fewer calories) than muscle does.
- Gender: Because men have proportionally more muscle, they tend to burn 10-20% more calories at rest than women do.
- Body Surface Area: As the ratio of body surface area to body volume increases, heat loss to the environment increases and our metabolic rate has to rise to replace the lost heat. So, if two people weigh the same, the taller person will have a higher BMR.
BMR Hormones: Leptin and Thyroxine
Discovery of the hormone leptin renewed support for the set-point theory. If our body's set-point acts like a thermostat, leptin seems to act as our thermometer. Normally, if we gain weight, our body produces more leptin, which shuts down our appetite, increases our energy output, and triggers other mechanisms that help restore our body to its set-point.
That's why fasts are not advantageous for weight loss. In one study, leptin levels in mice dropped 40% after a 3-day fast and 80% after a 6-day fast.
Our BMR is also greatly affected by how much thyroxine our thyroid gland produces. Thyroxine has been dubbed the "metabolic hormone." Within our cells, it increases our oxygen consumption and heat production, thereby increasing our metabolism.
Perhaps our future will hold the cure for some types of obesity through manipulation of these hormones.
Our Total Metabolic Rate (TMR) is one aspect of our metabolism that we can change. TMR is the rate of calorie intake we need to fuel all activity - voluntary and involuntary. Our TMR is largely made up of our BMR, but voluntary muscle activity, light or heavy, causes great leaps in our TMR and heat production. Food-induced thermogenesis (when we eat) also increases our TMR, especially when we consume protein or alcohol, probably because of the extra work our liver has to perform during these times.
In contrast, fasting or severe calorie restriction results in a drastic depression of our TMR, resulting in our body not breaking down our fat reserves.
Changing our Metabolism
In the meantime, although our set-point remains the same, we can adjust our TMR with continuous, long-term lifestyle changes.
Based on the factors listed above, we can't change our genetics or our gender, but we can reduce our stress levels, develop more muscle, increase our activity level, and, contrary to wide-spread weight loss plans, due to our set-point, we need to eat healthy meals without cutting calories drastically, which would only slow our metabolism. See: How to Lose Weight by Adding, Not Restricting.