PAll over the world, summer is synonymous with heat, water activities, cold drinks and, of course, ice cream. While most of us agree that ice cream and cold drinks are summer treats, do they actually help cool us down?
To find out, you need to know a bit more about how the body controls its temperature under different conditions. Maintaining it at an optimal temperature is done through a process called thermoregulation, which involves a delicate balance between heat production and heat loss.
Our species is said to be warm-blooded, endothermic, which is a scientific way of saying that we can control our body temperature regardless of the environment. We can do this because our bodies are constantly producing heat as a byproduct of internal chemical and biological processes (metabolism).
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The counterproductive effect of ice cream
This metabolism is necessary for the proper functioning of our body. It includes the digestive processes involved in the breakdown of nutrients in food, the absorption and transport of these nutrients to cells, and their conversion into building blocks or energy needed for physical activity.
All the chemical reactions that contribute to it can generate heat. It is beneficial when it is cold, but when outside temperatures rise, we must avoid overheating…
While it may seem logical that the introduction of a cold food into the stomach, such as ice cream, helps to reduce the temperature, its initial cooling effect is in fact quickly replaced by the heat generated by the digestive processes necessary for the decomposition of its nutrients. The digestion of high-calorie foods then leads to an increase in body temperature. Ice cream is therefore not the best option for cooling off.
But what about cold drinks? The transfer of heat between a cold drink and the digestive system can indeed directly influence the temperature… However, this is only momentary and depends on the quantity and the caloric content of the ingested liquid.
A small amount of liquid will quite quickly lose its cooling effect, being warmed by the surrounding organs. And large amounts of cold liquids will cause blood circulation to slow, making heat transport less efficient.
As you can imagine, high calorie drinks, such as sodas, will have a similar effect to ice cream and kick-start our metabolism soon after ingesting them.
Still, it feels like refreshing
This cooling effect of cold liquids is most likely explained by the rehydration they allow. If heat builds up within it, the body will attempt to lose excess heat by transporting it away from vital organs to the surface of the skin, where it is transferred directly to our surroundings by convection and radiation.
For this to happen, the ambient temperature must be lower than our own temperature, otherwise the opposite happens and heat is transferred to our body. Just like the heat radiated by the sun on a hot summer day.
Sweating is our most efficient way to lose heat. It occurs when an increase in the body’s core temperature is detected by the brain, which responds by stimulating the sweat glands spread all over our skin to produce sweat.
Once on the surface of the skin, this freshly transpired water evaporates, causing local cooling (also called evaporative cooling). The blood circulating near the surface of the skin cools in the process and helps reduce core temperature.
On average, an adult can lose up to half a liter or a liter of sweat per day, but in hot environments this amount can reach almost a liter and a half per hour. This is why it is essential to keep the body hydrated in hot weather.
What to drink then?
We have other drinks to try to refresh ourselves.
● What about alcoholic beverages ? Many people throw themselves on a cold beer on a hot summer day in an attempt to cool off… Bad idea, because alcohol is a diuretic. This means that it will promote the mechanisms of evacuation of our water via the urine and thus reduce your ability to lose heat through perspiration.
● Paradoxically, the hot drinks can be a good way to cool off. Although not intuitive, drinking a hot beverage triggers a sweating response in receptors in the mouth and throat, allowing the body to cool down without having to ingest a large amount of hot liquid. Our blood vessels dilate and help evacuate excess heat. Be careful not to become dehydrated as a result of excessive sweating.
● Some ingredients in spicy foods have the same effect; they also trigger a sweating response that allows the body to cool down. This is why these types of foods are popular in hot climates.
So while cold treats can be satisfying and certainly refreshing, a better way to sustainably cool down is to spice things up a bit, sweat it out, and most importantly, rehydrate!
Translated from English by Benoît Tonson with the help of DeepL.
* Peter Poortvliet, post-doctoral Research Fellow in Neuroscience, The University of Queensland
