I couldn’t find on the internet a complete, yet concise, technical explanation for how sugar makes us fat. Hopefully what I’ve pieced together below helps for anyone interested in the mechanisms.
Sugar, or sucrose, is a molecule composed of approximately 50% glucose and 50% fructose. Starting with glucose, lets look at how that affects the body.
The consumption of glucose triggers insulin release by the pancreas. Actually, even the anticipation of consuming food can be enough to trigger secretion.
Insulin then triggers a few hormone switches:
- Firstly lipoprotein lipase is ‘upregulated’. By this we mean it gets activated/switched-on. This hormone is distributed unevenly about the body. Genetics determine the distribution. Specifically men have more around their waist, women have more around their hips and breasts. It’s relative absence from say our hands and feet is the reason they don’t accumulate adipose tissue to the same extent as other parts of hte body. When upregulated it causes the body to pull fatty acids from the bloodstream into cells and store them for future use. If it pulls fatty acids into a fat cell then that fat cell gets bigger in size. When it pulls fatty acids into the muscle, the acids can then be used as an energy source. As you can imagine, having LPL regularly upregulated is not optimal. This causes us to constantly be in a state of fat storage.
- Secondly hormone sensitive lipase is ‘downregulated’. This hormone is responsible for lipolysis, that is, the breakdown of lipids into fatty acids. It’s the way our bodies utilise stored fat. This doesn’t just happen when we’re starving (a ‘rainy day’), it’s actually a process that happens continuously, particularly useful for when we go to sleep and need energy.
These hormone switches put our body into fat storage mode, thereby building fat stores and limiting the liberation of existing deposits.
However there is more; the fructose. It doesn’t trigger insulin secretion like glucose, and it is metabolised by the body quite differently.
Fructose metabolisation takes place in the liver. This is due to fructokinase, a key enzyme in the metabolism of fructose, being expressed only in the liver. Fructose gets converted into triglycerides, and these fatty acids are transported, via lipoproteins, for storage. The more fructose in the diet the higher the triglyceride levels in the blood stream.
The long term effect of high fructose consumption is increased insulin resistance. This is because fructose blocks the metabolism of glucose in the liver, and the synthesis of glucose into glycogen. This causes the pancreas to secrete more insulin to overcome the glucose traffic jam in the liver, and in turn the muscles become more insulin resistant.
Insulin resistance results in chronically elevated levels of insulin (the fat storage hormone) and therefore more time spent by your body accumulating fat.
When you put the effect of glucose and fructose together it’s possible to see how they would have a synergistic effect when it comes to elevated insulin levels and, longer term, insulin resistance and weight gain.
I appreciate it’s somewhat technical, but hopefully the above helps in terms of understanding how sugar makes us fat. I’m sure there’s more that I’m missing here, so if anyone has corrections/improvements, I’d welcome them.