It comes as no surprise that eating less often equates to an improvement in heat/humidity tolerance. Anecdotally, I know that on those days I eat a nutritionally dense diet yet maintain my caloric intake at a level required for weight loss, I can handle the 90-degree heat with 90% humidity just fine. That was my life today.
However, earlier this week, for whatever reason, I came home from my usual bike ride famished. The result, of course, is that I downed an insane amount of calories in a short period of time. While yes, my body metabolized it just fine, it generated insane amounts of heat and as a result I was a sweaty, intolerant mess. It was torture and pure hell. I have learned that if I want to stay cool in this heat then I need to watch the level of calories that I take in.
Whenever I notice interesting trends within my own behavior as it relates to my environment, I like to indulge in a little PubMed and see what the scientists have to say. I found this one article by Hall and colleagues which examined the effect of caloric restriction on thermotolerance in old rats. They hypothesized that caloric restriction would increase heat tolerance by reducing cellular stress and the subsequent accrual of oxidative injury. The researchers found that the calorically restricted rats survived intense heat exposure whereas only half of the control-fed counterparts did. The calorie restriction also reduced head-induced radical generation, stress protein accumulation, and cellular injury in the liver. The ultimate conclusion was that caloric restriction improves thermotolerance and reduces hyperthermia-induced cellular damage in old rats.
After reading and processing this information, I am lead to believe that heat generation in the body is additive. Now this makes sense to me because a food Calorie is simply 1000 kilocalories, which is a unit of heat measurement. Of course, if I consume calories then I can expect to generate heat.
I wonder then, why does eating far fewer calories result in no perceived generation of heat? A calorie is a calorie, right? I’d say that the perception of being “over-hot” is masked beneath some threshold of heat tolerance. The hypothalamus regulates body temperature based on the temperature of the blood coming into the area and maintains the optimum operating temperature for the body. This in turn affects the rate of the internal chemical reactions for the organism. Eating too many calories induces a type of hyperthermia as the body is absorbing all of the additional calories through digestion. Perhaps food is digested according to some CPG and thus, whatever calories are processed release their energy into the body and are absorbed. Because high calorie food contains a lot of energy, the digestion process releases a lot of heat, further continuing the processing of calories at an even higher pace now (assuming that with increased heat you get faster chemical reactions). While the reactions are now faster, perhaps they are now less optimal and residuals of such a fast breakdown are not only the physically noticeable side-effects of sweat and reduced heat tolerance, but also things like stray free-radicals being released into the body, inducing things like cellular oxidation.
This means I have a threshold of heat that my body can absorb, and beyond that it will do its best to release it into the air. Alright then, could exercise induce the release of free-radicals also? We are increasing the core body temperature and thus theoretically inducing hyperthermia.
In this case, I think that the chemical processes are different. In the first case the release of calories is in the digestion phase and additional energy is being stored in fat cells. In the latter case though, the release of calories is not from the digestive processes (which are actually resting during exercise) but actually from the breakdown of glycogen and fat chains. The fat chains may not release as much energy as when carbohydrates are broken down at meal time. Also, with the digestive system at rest, more resources can be pooled to take care of the breakdown of stored energy. The chemical reactions to break down food are different than those needed to breakdown fat, and thus the residuals and corresponding limiting factors for a cascade of related processes, are different as well.
Because the stored energy is being broken down, free radicals would not be released in the same way.Now that the body is looking to breakdown stored energy, instead of simply breaking down new food Calorie energy, the processes do not yield the same chemical by-products.
Eating less not only assists with thermoregulation, but also with hormone regulation and metabolism in general. With a slower metabolism and slower release of hormones, chemical processes are not overwhelmed creating byproducts as the result of an inefficient temperature for the reactions. I guess its easier to put on a sweater to stay warm than it is to take off clothes to stay cool (I mean, you can only take off so many clothes!). The same idea applies to the human body.
Therefore, caloric restriction helps my hypothalamus maintain an optimal operating temperature for my body’s chemical reactions. By maintaining a slightly cooler set-point, I am allowing for some margin of error for heat absorption which results from eating food Calories. I don’t allow myself to hit the threshold for inefficient reactions to take place. I can absorb heat without perceiving discomfort. Digestive chemical processes are much different than glycolysis and lipolysis from fat cells, and thus one is more harmful than the other( thats not to say that lipolysis is any less harmful as being overweight blocks many of the benefits of calorie restriction due to the hormones fat cells release).
So, I don’t know, but this mini-search has motivated me to be careful with the amount of food calories I eat at a time. Large indulgences are not healthy and digesting such copious amounts of food is really taxing on the body. It is better to slow the metabolism and slow the release of hormones – like titration. You don’t just want to dump your reactant into the solution, you ought to titrate it, or else you will end up with a mighty unstable solution!
