Not all fat in your body is equal, and where the fat is deposited is a surprisingly important determinant of health. Photo / 123rf
Research shows that lower levels of visceral fat are predictive of good, long-term health – and you have the power to reduce yours.
Like many people, I see fat in parts of my body that I would rather not have. Although many of us consider all body fat as bad, this is not true. Fat is essential for health. Aside from providing energy and keeping you warm, fat is vital for building cell membranes, synthesising key hormones and absorbing certain nutrients. Fat storage was key to our survival as a species.
However, not all fat in your body is equal, and where the fat is deposited is a surprisingly important determinant of health. Belly fat is a good example of this.
Whether you are working hard to reduce it or have given up and are watching it steadily expand, belly fat is something everyone is conscious about. Most of us consider fat around the middle to be the same as fat under our skin, on our hips or elsewhere. The latest science, however, underlines how very different it is: belly fat is a glimpse into our future and longevity.
It is hard to ignore that people deposit fat in different parts of their bodies. While some seem to store most of their excess energy around their buttocks, others tend to keep it around their belly.
Around 20 years ago, while studying twins, we found that these differences in fat deposition are highly genetic. Whatever their weight, identical twins had very similar shapes. Also, they vary significantly between males and females.
In females, genes seem to decide whether the fat goes mainly to the thighs and bottom or around the belly, giving the so-called apple and pear shape stereotypes. This novel finding and the headline-worthy fruit terminology helped us make the headlines in many papers, with references to the “healthiness” of Marilyn Monroe and Jayne Mansfield.
Since then, we’ve learned even more about the differing roles of fat in these areas. In general, and particularly in females who have more of it, fat stored around the buttocks and thighs is much healthier and protects against heart and metabolic disease.
These fat deposits keep energy locked away for a rainy day and don’t interfere with your body’s metabolism. It is nature’s way of protecting females of childbearing age, ensuring they don’t run out of valuable resources during pregnancy or breastfeeding, a critical, often energy-draining time.
In contrast, belly fat, which is often nestled around your liver and intestines, is metabolically much more active, closely linked to your blood levels and behaves very differently from the fat in other parts of your body.
Belly fat, more accurately called visceral fat, increases the risk of many conditions, particularly type 2 diabetes and heart disease. It does this by interfering with how your body responds to glucose and insulin.
Compared with females, males have on average more of this central fat, so when they gain weight they are more likely to be apple-shaped. Evolutionarily speaking, this might be related to their duties of walking long distances and fighting, as belly fat can be converted into energy in an emergency more quickly than fat elsewhere.
Also, food scarcity in the past was a real threat to survival, particularly for children. This evolutionary pressure may have driven females to develop their specialised fat stores, whereas men, who are much more expendable in evolutionary terms, did not.
Whatever the reason, males’ propensity to lay down visceral fat is one of the reasons we are more at risk of heart disease during midlife than women. This is despite the fact that women overall have a higher percentage of body fat.
In contrast, females tend to only lay fat down around their abdominal organs once the healthy stores in their buttocks and thighs are full. Similarly, once abdominal stores reach maximum capacity, fat starts overflowing in organs like the liver, heart and pancreas, and even muscle, where it can interrupt their normal functioning.
Another important factor in fat distribution is the influence of hormones. Oestrogen is particularly important in females. So, as oestrogen levels drop during the menopause transition, weight gain around the belly is more likely.
Understanding how much visceral fat you have isn’t just a case of looking in the mirror. To assess it properly, we need to use Dexa scans, first used to detect weak bones associated with osteoporosis. I have been measuring twins for over 30 years and these Dexa scans have taught us that often, visceral fat is invisible from the outside.
Some men who look relatively slim still have significant amounts of visceral fat inside. This has earned them the nickname of TOFIs, an abbreviation for “thin on the outside, fat on the inside”. My colleague at Zoe (a company that uses data-driven research to help improve health), Jonathan Wolf, was upset when I called him (accurately) a TOFI when I arranged for a scan six years ago.
As we age, we are more likely to accumulate visceral fat. My own levels, like my belt size, steadily increased without me noticing, until I started taking my health seriously around 12 years ago.
Since then, I’ve reduced my visceral fat levels (and belt size) through dietary changes, and no doubt added more healthy years to my life. There is plenty of research from our group and others that lower levels of visceral fat are predictive of good long-term health.
This month, Zoe published a clinical trial in Nature Medicine which found that, compared with people who followed standard dietary advice based on lowering fat content and limiting calories, those who followed Zoe’s advice significantly reduced their waist circumference – a marker of reduced visceral fat. This was a bigger effect than overall weight or general measures of obesity like BMI.
This is a good sign that you can reduce belly fat by enhancing the quality of your diet and making smarter food choices based on your individual gut health, blood sugar and blood fat responses.
So, although there are genetic tendencies to deposit fat in certain parts of your body, you are not predestined to deposit it in unhealthy sites. Through dietary changes and keeping physically active, you still have the power to reduce your belly fat.
Next time you look in the mirror, think not only about what is skin deep but also what lies within. We need to be less obsessed with our outward appearance and treat our inner self with the respect it needs and deserves.
Tim Spector is a British epidemiologist, medical doctor and science writer.
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