Food and Thermogenesis: How what you eat affects your body temperature

Energy produces heat. If you didn’t sleep through science class, they probably taught you this.

There are all sorts of circumstances behind what we now call climate change, the steadily rising temperature of the planet. But one key element is the fundamental existence of more human beings than have ever been on the planet in recorded history.

All humans produce heat. Every mechanical, electrical, chemical anything we have ever done produces heat. Vehicles and other machines produce heat when they operate. Anything we built that moves produces heat. Even the coldest fridges, freezers and air conditioners produce heat to cool what’s inside: The heat is just emitted out of the back or top of the device into the surrounding atmosphere.

And our bodies produce heat. The bigger we are, the more active we are, the more heat we produce. This is a key reason why your perceived temperature is hotter when you’re running than it is when you’re walking or still. You produce a lot more heat when you exercise.

Even the energy required to digest food produces heat. The act of digestion producing this energy is a little something scientists call thermogenesis.

Some foods require more energy from thermogenesis than others. This is one of the keys behind why it’s generally healthier to eat unprocessed meat and vegetables than processed sugar.

Insoluble fiber and most proteins require a lot of digestive energy for the body to digest its nutrients. These foods are highly thermogenic.

Meanwhile, chemically refined sugar is by design quickly digested, as these foods are chemically engineered to not satisfy you hunger and make you crave more of them. These foods are lightly thermogenic.

You can eat 500 calories of sugar cookies, and still be very hungry immediately after eating them. Meanwhile, you can eat 500 calories of steak, and be so full you won’t want another bite of anything for several hours. And woe is the poor soul who tries to eat 500 calories of broccoli… if he even manages to get it all down (1 cup of cooked broccoli is about 60 calories). He will end up spending a regretful amount of time on a toilet at some future point.

Broccoli and other vegetables are among the most thermogenic of foods. Many require more caloric energy to burn them than the calories the vegetables themselves contain!

Now, why bring up global warming when bringing up the thermic effect of food? Is Steven saying that broccoli causes climate change?

No, not at all. I brought global warming up to highlight that everything that requires energy from a human has a warming effect. Theromgenesis requires energy, and the entropy of that energy produces heat.

For people, this matters more specifically when in situations where they want to produce heat… or not produce heat. I can think of a few distinct situations.

Non-athletically, I’m simmering through an obvious one: I’m in Las Vegas in the middle of summer, and it’s very hot. Like anyone else here, I’m interested in finding ways to minimize heat and stay cool.

One thing we don’t consider is the effect of our food on heat generation.

Because I train a lot and I’m a man, I eat a lot of protein. Because I want to eat healthy, I do eat a fair share of vegetables.

Both of these foods are highly thermogenic… meaning they produce a lot of heat. The more of these foods I eat, the hotter I am going to get. This is a problem during summer when I’m trying to cool down.

Now, this is not a license to go and eat a bunch of processed sugar or other lightly thermogenic foods that probably aren’t good for me in most situations. In fact, there is one dietary move (aside from drinking cold water) that is even less thermogenic: Eating nothing at all. Such as: Intermittent Fasting.

Obviously, I need to eat at some point every day and bite the bullet on, basically, getting hotter. I can’t just starve 24/7 without eventually dying. That said, and aside obviously from respecting my nutrient needs, I should be mindful of the timing and placement of my meals. For example:

  • It’s probably best to have that first meal if/when it’s not as hot, or indoors in a fairly cool place where I know I won’t need to face extreme heat for a while
  • It’s probably best not to exercise outside in high heat right after a highly thermogenic meal, e.g. protein and vegetables
  • If I know my sleeping conditions are a bit warm, I will either want to make sure not to eat too much protein or fiber… or to eat the meal early enough in the night that it’s had some time to digest, ideally in a cooler environment, before I hit the hay.

Conversely, during winter, I can use this to my advantage to help warm up.

  • If it’s super cold outside, that’s a good day to eat several meals with a lot of protein, vegetables and other insoluble fiber. The high thermogenic effect will help warm me up.
  • If I’m going to exercise outside in those conditions, a highly thermogenic snack can help amplify my efforts to stay warm during exercise.
  • Likewise, if it’s somewhat cold in my bedroom, I can eat a big protein rich meal before bed knowing it will help amplify my body heat at bedtime through the thermogenesis.

This also highlights why many people find it beneficial to drink Gatorade and consume gels or other quick-burning fuel during exercise. When you’re hot from exercise, and you need fuel, the best fuel is that which burns quickly and is not very thermogenic… not just to get it into your bloodstream ASAP, but because it generates less additional body heat.

Likewise, if exercising outdoors in the dead of winter, it may benefit you to fuel with something a little more fiber or protein rich (if your stomach can handle it when training), at least before or as you begin training. The increased thermogenesis will help offset the extreme cold’s effect on your body as you try to warm up.

When thinking about training goals that involve high protein (e.g. gaining muscle and strength) or fat burning (e.g. more vegetable and fiber intake)… those foods’ highly thermogenic effect also in turn suggest:

  • Summer may not be the best time to add strength/bulk, nor to try and burn fat, because both tend to require foods that produce high thermogenesis, which makes you hotter. Given summer’s already hot, you want to avoid making yourself hotter unless you have the privilege of tightly controlled conditions where you can recover in a normal temperature setting for most of your day. In that case, extremely hot conditions could benefit you by amplifying fat burning and mitochondrial development from training in heat. (This served Jerry Tarkanian’s UNLV basketball squads well in the 70’s-90’s as they often trained outdoors in the Vegas summer… but also spent the rest of their time in the campus’ air conditioning when not training.)
  • Likewise, winter may actually be the best time to add strength/bulk, or to try and burn more fat, because the high thermogenesis of the needed foods will be quite welcome in the cold conditions.
  • However, this is very counterintuitive. First off, major winter holidays are build around consumption of sugary, fatty, typically unhealthy foods. It’s harder to adhere to a healthy, whole food diet amidst Halloween, Thanksgiving and Christmas dinners. Also, in many parts of the country, it can be hard to train outdoors in winter due to icy conditions, snowfall, and dangerously low temperatures.
  • At the same time, summer is a great time of year to maintain your weight by moderating intake of those and other foods, plus is the best time to ingest more quick-burning sugars and thus is a good time for endurance training. This does line up with the traditional spring-to-fall peak running season in most locations. The only issue is when living in extremely hot conditions, such as my case with Las Vegas, where it may be impractical to train regularly as an endurance runner.
  • That said, you can work on burning fat in summer, if instead of maximizing protein/fiber intake you focused mostly on intermittent fasting, which is the least thermogenic of your diet options. However, instead of gorging on protein during your feed window, it would be prudent to spread your protein inatke out across multiple smaller, more frequent meals… and perhaps have a shorter fasting window of 12-14 hours to facilitate frequent meals.
  • Summer may be the best time of year to practice the traditional post-modern athlete’s diet of many small meals per day instead of 2-3 meals per day. And winter may be the best time to eat a handful of larger meals for your fuel.

I’m not going to draw any strong conclusions from this, as it’s a fairly new idea for me. This is something I’m going to tinker with going forward.

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