Reporter: Vishnu Gopinath
Video Editor: Abhishek Sharma
Medical Expert: Dr. Ashwini Kumar Setya
India is no stranger to extreme temperatures. Heatwaves, cold snaps, long fiery summers, and icy cold winters are a part of living in the world's largest democracy.
If you've ever experienced both hot summers and cold winters, you'll know what we're talking about - how in the winters you feel like eating constantly, and often rich, fatty, and indulgent food.
While in summer even just the thought of eating a rich, fatty meal can make you feel uncomfortably full.
So, what gives? Why do we lose our appetite in the summer? Why does winter automatically trigger a craving for warm, wholesome food? And how does heat affect your appetite?
Let's find out.
To understand how heat affects your body you need to understand two concepts - thermoregulation and thermogenesis.
Thermoregulation - The word 'therm' comes from Greek, meaning heat.
Thermoregulation is the process through which warm-blooded mammals maintain their core temperatures. We've already discussed what happens to the body under extreme heat.
But a short refresher: The human body's internal temperature is around 36.8°C, give or take 0.5°C. If your internal temperature rises or falls by 2-5 degrees you can suffer hypothermia and frostbite (if it's too cold) or hyperthermia and heatstroke (if it's too hot).
When outside temperatures fall below your internal temperature, your body compensates by warming itself up. When the outside temperature rises ABOVE your internal temperature, your body sweats in an attempt to cool itself off.
Many factors affect your internal temperature, these include:
Exercise or activity
Food, is one such key factor that affects your body's temperature. This is where we bring in the second concept - thermogenesis.
Thermogenesis is the process of metabolic activity generating heat.
Activities like eating and exercise generate heat as a by-product. That's why, when you get moderate to intense physical exercise, you start to sweat. Your body generates heat, and you sweat to cool yourself off and regulate your internal temperature.
The food you eat heavily affects your core temperature as well. Some foods generate more heat when digested, while others less.
This is known as the thermic effect of food (TEF) or diet-induced thermogenesis (DIT). The amount of heat generated as a byproduct of foods varies based on whether you're consuming fat, protein, or carbohydrates.
Additionally, the water content of your food also affects its thermic effect. A 2004 study reported the following about different nutrients and their TEF:
"Reported DIT values for separate nutrients are 0 to 3 percent for fat, 5 to 10 percent for carbohydrate, 20 to 30 percent for protein, and 10 to 30 percent for alcohol. In healthy subjects with a mixed diet, DIT represents about 10 percent of the total amount of energy ingested over 24 hours."
So, in short, the nutrients in the food you eat will generate different amounts of heat and warm your body to a different degree.
Fat and protein tend to be more thermogenic than carbohydrates, and as a result, they'll make you feel hotter after you eat them, even sweating to cool yourself off sometimes.
That's why you'll experience something called the "meat sweats" - where you sweat after eating a meal loaded with protein and/or carbohydrates and fat.
That's why you don't feel like eating rich fatty meat too often in the summers (especially if you live in a tropical country like India). Your body just becomes uncomfortably hot.
Now as your core temperature rises, you'll progressively experience more discomfort. Again, we've covered what your body experiences as your internal temperature rises, in this video.
In short, discomfort, fatigue, confusion, dizziness, muscle cramps, dehydration, and in severe cases, heat stroke, organ failure, and even death. So, to protect you from overheating, your appetite for heavy foods with a high thermogenic effect goes down.
You still experience hunger if you don't meet your daily energy requirements, which is why you'll still feel hungry, but won't have a large appetite (unless you work out or get a moderate amount of exercise).
This isn't just feels-based or pseudo-science, it's been studied and proven that humans eat lesser as the heat rises.
Take for example this excerpt from a 1947 study on the effect of heat on the appetite of soldiers in different geographical regions.
The study found that the food intake of soldiers and infantry troops from the Canadian Arctic to the tropical Philippines varied despite both groups being offered as much food as they wanted.
Troops in the tropics ate on average 3100 calories a day while troops in the arctic ate an approximate 4900 calories a day.
The same was confirmed in 1964 with another study observing a 25 percent decrease in food intake by soldiers in Yemen as compared to soldiers stationed in the United Kingdom.
"There's an interplay of energy expenditure either to keep the body warm or to keep it cool. Your body spends energy in this process. When it's cold you expend energy to warm yourself up. And you usually need more energy to warm yourself up than cool yourself down. That's why in the summers we don't crave foods with high energy loads - like fat-rich food."Dr Ashwini Kumar Setya
Additionally, Dr. Setiya adds, we tend to sweat a lot in the heat, losing as much as 1.4 litres of sweat per hour of exercise.
You lose a lot of electrolytes during this process, and like we've mentioned before when you lose electrolytes like sodium, your body desperately tries to regain these lost electrolytes and fluids.
And it just so happens that a lot of low-calorie foods like fruits and cruciferous vegetables tend to offer the fluids your body craves.
So, in short, people tend to eat more in the cold, craving food that's rich and fatty, and less in the summers, when they're already trying to limit the heat they have to endure.