From releasing hormones to regulating our temperature, fat has myriad roles in the body. Here’s why chasing extreme fat-loss goals is so unhealthy. Fat has been somewhat demonised for years. Diet culture tells us to burn it, some food companies market low-fat products at us, and weightlifting forums share tips on how to reach as little body fat as possible. You only need to spend a moment scrolling through social media and you’ll soon find advice on how to “get shredded“. This sinewy physique is defined by extremely well-defined muscles.
This year, experts are concerned that the trend to be super skinny is once again resurfacing, in some cases fuelled by the popularity of weight-loss drugs. Yet while too much fat poses health concerns and can lead to obesity, too little is not good for us either. The goal of ridding ourselves of fat can be damaging biologically as well as socially, numerous experts have told me.
So how much do we really need? And why is too little body fat bad for us?
Why body fat matters
Broadly speaking, there are two different types of fat: dietary fat and body fat. Dietary fat is the fat you eat in your food, while body fat is nature’s way of storing energy you don’t need.
When you eat a meal, the dietary fats, carbohydrates and proteins in the food are broken down into simple building blocks your body can use for fuel. Carbohydrates become glucose, proteins become amino acids and fats become fatty acids. If you consistently eat more calories than you consume, fat cells – known as adipocytes – store these excess nutrients as lipids. This causes the fat cells to expand in size.
However rather than just sitting there passively, we now know that body fat is an active organ which regulates the body’s functions. Just like in the story of Goldilocks and the three bears, our body works best when things are “just right”. Too little, just like too much, is dangerous for our health.
We can think of our body fat as a specialised storage vault, taking up nutrients when energy is abundant and releasing them only when needed. It’s a system that helped our ancestors survive periods of food scarcity.
Another important role is communication. Fat cells produce hormones that tell the rest of the body how much energy we have and how full we are. The best studied of these is leptin. Leptin tells the brain there is sufficient energy storage, and then the brain can almost relax, which leaves the body able to focus on important biological processes such as reproduction and fighting infection. Without leptin, the brain starts to worry about the amount of energy available, meaning essential functions start to be deprioritised.
Body fat is also important for staying warm. While white fat stores excess energy but also acts as a layer of insulation. Meanwhile, brown and beige fat contain specialised cells that burn energy to produce heat. This helps the body maintain its temperature.
What happens when we have too little?
The health consequences of having too much fat are well known. They include an increased risk of cardiovascular disease, type 2 diabetes, certain cancers and osteoarthritis. However, having too little is not good either. When body fat drops too low due to severe calorie restriction, it can have profound effects on our health and physiology.
When the body has too little fat it responds by trying to save energy, essentially putting itself into starvation mode. Systems start to shut down, including our immune function. With no reserves left, the body starts to break down muscle instead. Bones are no longer built and repaired.
This results in frailty and increased risk of fractures.
Too little body fat can affect our hormones and reproductive health too. In men who become extremely lean because they are chronically under-fuelling themselves, testosterone can fall, as can energy levels and physical performance. Some female athletes with very little body fat experience irregular periods or find that they stop altogether.
How much do we really need?
It’s surprisingly tricky to measure how much body fat you have yourself – but more on that later. There is also no universal percentage to aim for. Individual needs vary. Nevertheless, as a broad guide, healthy adult men tend to have around 10–20% body fat. Healthy adult women tend to have around 20–29%. Those living with obesity tend to have body fat above 30%.
In terms of how much is optimal, this might differ between people, sex and ethnicities. Among athletes the typical amount of body fat tends to be lower.
It also matters where you store fat. Visceral fat, also known as belly fat, is especially harmful if you have too much of it. Unlike fat that lies under the skin, visceral fat wraps around vital internal organs and releases inflammatory chemicals that raise your blood pressure, and interfere with insulin, making it harder for the body to control blood sugar and raising the risk of type 2 diabetes.
Credit: bbc.com
