Where we store fat and why

Factors determining where we store our fat

• Genetics – research has shown that our genes hugely affect our body shape [1, 2]. Which may be no surprise if you're someone who shares the exact same body shape as your mother or father! It's estimated our genes determine around 75% of our body fat distribution [2] – so the lion's share. But while we can't do much to change our predisposed body shape and where we store most of our fat, lifestyle factors do play an important role and we have some control over how much fat is stored.
• Sex – males and females not only store fat differently, but they also store different amounts of fat. Women typically have a higher body fat percentage than men and also tend to store more fat around their hips and thighs, as well as in their breasts – whereas men have a tendency to store excess fat around their middle [3]. It's theorised that this additional fat storage and more typical distribution around the lower body may be protective during pregnancy.
• Hormones – our hormones appear to play a role in fat storage and distribution and may explain some of the differences between men and women. In one review it's stated that oestrogen was found to help reduce fat storage, and that inhibiting oestrogen production results in increased fat storage in men, as well as women [4]. Testosterone was also stated to have fat reducing properties, with reduced levels of testosterone associated with increased abdominal fat storage [4].
• Age – as we get older, we do tend to start storing more fat, simply because our metabolism begins to slow due to age-related muscle loss. This does mean that weight loss and maintenance can be more challenging, but it is still within our control to modify our eating and exercise habits to try and counterbalance our reduced calorie needs.

Other factors affecting fat storage

• Diet – while the main factor for fat gain is consuming excess calories, the types of foods we eat do have a bearing on where our body will store some of the excess fat. High-sugar foods lead to a rise in insulin levels – the hormone responsible for maintaining healthy blood sugar levels. If we eat lots of sugar from foods that are quickly digested and absorbed, our insulin levels will be frequently raised. Insulin promotes fat storage and inhibits fat breakdown, so high circulating levels of insulin over time can lead to excess fat storage. Interestingly one study also found that participants who ate more saturated fats gained more fat around their liver and abdomen, whereas unsaturated fats lead to more even fat gain across the body – when both groups were overfed with each nutrient for 7 weeks [5].
• Lifestyle – it's probably no surprise to hear that inactivity can lead to increased fat storage. Of course, regular exercise helps burn calories to help with weight management. However, one study also found that the amount of time spent being sedentary was associated with an increased waist circumference [6]. This indicates that inactivity can directly encourage more fat storage around the abdomen.
• Stress – high stress levels can cause the stress hormone cortisol to increase. An increase in circulating cortisol levels is believed to contribute to higher abdominal fat storage during times of stress [7]. It's unclear why this relationship exists, but it is wise to try and manage our stress levels to help avoid excess fat storage around our middle.

Types of fat

The reason why we're interested in where we store fat is because this can indicate our risk level for certain health concerns. We have different types of fat within our body, and where we visibly store most fat can highlight which type we have more of, in some cases.

• Visceral – this is the type of fat we're most concerned with from a health point of view. It is stored around our organs, deep within our body and isn't visible by just looking at someone. However, more fat around the abdomen is associated with a higher level of visceral fat. Too much fat around our organs can put us at increased risk of cardiovascular disease, diabetes and some cancers.
• Subcutaneous – this is the type of fat we can see and feel as it sits just below our skin. It's visible around our arms, legs, bum and belly. This type of fat isn't as concerning as visceral fat, but high levels are still associated with an increased risk of health complications. It is possible to have high levels of subcutaneous fat, without having high visceral fat – but this isn't common. Likewise, it's possible to have low levels of subcutaneous fat and high levels of visceral fat, so just because a person appears slim doesn't mean their lifestyle may not still be putting their health at risk.
• Brown fat – this is a unique type of fat that adults have in very small amounts, but babies have in large amounts. It's mostly responsible for keeping us warm when exposed to cold temperatures and it does this by producing heat, which uses calories. This means brown fat actually burns calories in the same way that muscle tissue does, so it's a bonus to our metabolism. Some research suggests we can increase our levels of brown fat through exposure to cold temperatures [8]. So a short winter walk without too many layers could help give your metabolism a bit of a boost!