This is how I understand it:
When we eat fats, they are metabolised into free fatty acids, taken to the liver and converted into triglycerides. Fine.
When we eat carbs, they are digested into glucose some of which is directly used by muscle cells and other cells of the body and the rest is taken to the liver and converted into triglycerides and some into glycerol. Okay.
So eating both carbs and fats should pile on the weight if we’re consuming more than our cells need, right? Well, it isn’t so simple.
Given a set number of calories in a so-called ‘balanced diet’ – let’s say bang on the average – (and keeping protein constant), consuming both fats and carbs seems to be a recipe for slowly but inexorably putting on weight. With the same set of calories, consuming relatively more carbs (even ‘good’ carbs) and cutting down on the fats to keep the calories constant, most people will still put on weight, maybe even faster. With the same set of calories, consuming relatively more fats and cutting down on the carbs, most people will stop putting on extra weight and some will take it off. Those are facts and they’ve been demonstrated over and over again.
If you cut the fats, you have to diminish the calorie count significantly to take off weight. That’s why such a way of eating is called a ‘semi-starvation’ diet. A period of weight loss is usually followed by a period of weight gain. More than before. Most people lose energy on such a diet and muscle mass as well. So, it’s not particularly effective and it is not easy to follow for many of us, yet still it is the most recommended diet around.
If you cut the carbs down, you don’t have to diminish the calorie count. The extra calories can be fats (and in our hypothetic situation, they will be); it doesn’t seem to matter, you will stop gaining weight and maybe start to take some of it off.
Maybe it has something to do with glycerol phosphate. And glycerol phosphate is manufactured from carbs. If glucose is burned by the cells, glycerol phosphate is produced. Glycerol Phosphate is used to turn fatty acids into trigycerides (yup, fats) and that’s necessary to put fat into fat cells. Carbs.
And maybe it has more to do with insulin. Eating carbs stimulates insulin release from the pancreas. Insulin has a number of activities, but its most prevalent use by the body is to pack triglycerides (fat) into cells. Yes, one of the effects of lowering blood sugar and packing fats into cells is to fatten us up. Eat something heavy in carbs (breakfast cereal, sandwiches, spuds, rice, fruit juices, fizzy drinks etc.) and insulin is secreted.
The problem is that a heavy carb intake load ups the blood sugar dangerously. The human body can only function in a narrow band of blood sugar levels or vital organs (especially the brain) can be badly affected. So insulin is needed to cope with this heavy carb loading we have self-inflicted. And it does. It removes blood sugars by shoving triglycerides into fat cells. As the levels of blood sugar decrease, insulin production drops off. Eventually, there is not enough insulin putting fat into fat cells to counteract the fat cells giving out fatty acids for the cells of the body to use as fuel (fat cells are really active cells). And the cells of the body quite like using fats for fuel and there is nothing unphysiological about the process. It happens in you and me all the time.
But if your insulin surge was big and fast enough, it drops just as quickly leaving the body depleted of blood sugars and without enough fatty acids being released from the fat cells to compensate. What happens? You get hungry. Somebody called it ‘internal starvation’.
One famous study had people on huge amounts of calories every day – up to 10,000 calories – up to five times normal. But these calories were from fats and proteins. Then, for experimental purposes, some of the subjects were asked to eat a meal of carbs in addition to their heavy fat and protein intake.
Believe it or not, those people became hungry a few hours after the carb ingestion. Even with all those calories! All due to that surge of insulin which was produced to lower the blood sugar level after eating carbs.
Carbs make us hungry.
Carbs make us put on fat.
Physiologically, we don’t need any carbs other than those found in green and yellow veggies.
If you’re interested in the scientific background to eating the low-carb way, check out FULL STOP – eat until you’re full and stop gaining weight.