In recent years high-fat diets have become increasingly popular as carbs have fallen out of favour in the world of health and fitness. It is true that high-fat diets can have some advantages in terms of fat loss, especially when combined with high protein intake as these nutrients help keep you fuller and therefore reduce overall calorie intake… however, there are some BIG myths that seem to have cropped up surrounding dietary fat intake and high-fat diets and the mechanisms by which they are supposed to work.
Why are no carb diets so popular?
The reason why carbs have become the ‘enemy’ in some people’s eyes is because it raises insulin levels. Insulin stops the release of stored body fat so that other nutrients we have just digested can be more favourably taken up into cells. Therefore carbs and insulin get blamed for weight gain as body fat can’t be used as a fuel.
Now, this is a VERY over simplistic view of metabolism and without getting into the nitty-gritty of it here, carbs are not directly to blame for weight gain or prevention of weight loss. That is all to do with energy balance no matter where the energy comes from. However, this idea of keeping insulin levels low has led to some people to believe that by simply keeping insulin levels low that fat loss can be attained regardless of how much fat we eat simply because fat does not raise insulin levels.
According to this theory, even if you ate 5000kcal a day of fat then you wouldn’t gain body fat because your adipose (fat) cells can still be releasing body fat to be used as energy! BUT this is only one side of the coin, just because your body can release body fat stores does not mean it is being used for energy and if you do not place a demand on the body to use that energy, through increased activity levels then you will gain body fat... it is not just about fat breakdown, it is about fat usage as a fuel as well.
So what happens to the 5000kcal of dietary fat I have consumed if I don’t use it? Simple really it will be stored as body fat, it has to go somewhere and it can’t just float around in the blood stream, as fatty acid levels in the blood would get larger and larger (this would not be good at all for health) as we consume more and more fat that is beyond our energy requirements and instead it needs to be taken out of the blood stream and stored for future use... and guess what the store is? Body fat.
So what would happen in a high carb diet?
In this situation it may seem on some level that fats will make you fat, but if we had the same energy excess as the example above but this time the diet was low in fat but a VERY high proportion of carbs, then as the body can only store so much carbohydrate as glycogen it is then forced to convert glucose into fatty acids (which takes place in the liver), which are then shuttled off for fat storage in our adipose cells. This shows that fats can make you fat but so can carbs, or any mixture of the two if you are in an energy surplus and therefore overall energy balance is the key determinant of fat loss or weight gain no matter where we get those extra calories from.
What about normal diets?
In normal situations what we tend to find is that in an energy surplus caused by a mixed intake of food, is that it is not carbs that are converted to body fat, but it is a combination of elevations in insulin that stop fat release combined with the storage of dietary fat that leads to fat accumulation. In fact even in periods of calorie restriction, after a meal, there are short periods where we are in a ‘storage’ mode (from either carbs, fats or a combination), it’s just that after these periods we then release fat from fat cells to make up for our energy deficit.No matter which way we cut it, or the nutrients involved, it is energy balance that determines weight loss or weight gain, not some magical properties of fat that on further scrutiny, and understanding of metabolism, just don’t quite hold up.
Thanks for reading, Dr P.
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