For a long time we’ve been told that carbs make you fat, and anecdotally you might have even found that you lose weight when you restrict the amount of carbohydrates you eat. There is, of course, the fact that carbohydrates store water - or to be more exact, glycogen, which is what carbohydrates are broken down into and stored as. Glycogen is stored in the muscles and liver alongside 2 or 3 molecules of water for every molecule of glycogen. So the old adage “you’re only losing water weight when you cut carbs,” is partially true.
Sugar has been demonized as the root cause of obesity and diabetes and carbohydrates = sugar. Insulin, when produced in excessive amount such is the case when we eat a high carbohydrate meal, especially when it contains lots of free sugars, promotes fat to be stored and inhibits fat breakdown in our adipose tissues. It also stimulates our bodies to use carbohydrates as fuel in our muscles, rather than using fat as a fuel, so as a result not only does insulin promote the storage of fat but it stops fat burning too. So the theory goes that by cutting down on carbohydrates you also decrease the effects of insulin and therefore lose weight. Whilst you might, anecdotally, find this to be the case there is actually much more at play here.
Is insulin really the driver of fat storage?
Like all good relationships, it’s complicated. Insulin does indeed promote our bodies to store fat, but to actually accomplish this process the body needs both fat and carbohydrate to get it done. So, let’s say you ate a purely carbohydrate diet (very unlikely, and very unhealthy), although your body can make some fat in the liver, it would never be enough to actually store any of the carbohydrate as fat. The second debunk to this insulin = fat storage hypothesis is that even if you were eating no carbohydrates whatsoever you would, in fact, still produce insulin as certain amino acids found in protein, leucine especially, prompt our bodies to secrete insulin. And protein is essential for our existence, so it seems unlikely that you’d ever be in a situation where no insulin at all was produced. In this scenario though, the amount of insulin released wouldn’t be sufficient to prompt any significant fat storage.
It’s much better to be low carb than it is to be low fat
Well, firstly, let’s just rejoice over the fact that finally the age of fat victimisation is over and we can all fully appreciate the essentiality of this macronutrient in our diets. Pass the peanut butter.. Specifically looking at weight loss, though, and not overall health in general, a study published in the American Journal of nutrition and carried out in very strict and controlled conditions showed that there was actually no difference, in terms of weight loss, between a low-carb and a low-fat diet; completely contradictory to the carbohydrate - insulin model above. The reason that most studies, which are less strictly controlled, show a much more significant weight loss in low-carb diets as opposed to low-fat diets is because carbohydrates typically include all the highly addictive foods that we find it easy to overeat; cakes, sweets, pastries, chips, crisps and chocolate. To name a faw.
So what’s actually going on?
We’re overeating. In most clinical trials that aren’t strictly controlled there is significant (about 20%) underreporting of how much food is actually eaten. In less civilized populations diets can typically be very high in carbohydrates, maize, rice and cassava for example, and sugar, and yet the population is not overweight or suffering with any of the Western health concerns such as diabetes or cardiovascular issues. In the West our consumption of saturated fat is still, in most places, too high and at the same time as eating too much fat our intake of carbohydrates is also adequate (i.e it is not low). What we end up with is oversupply of both carbohydrates and fats, essentially too much food in general, which is what’s really at the root of the problem. Not carbohydrate itself.