I was having a conversation today and not able to explain that the body uses proteins to make what it needs through a process called
gluconeogenesis Dr. Jason Fung writes about this below:(excerpt from Diet doctor.com)....
"What happens if you overeat protein?
So what happens to the excess amino acids? They cannot be stored directly as energy, so they are converted to glucose via
gluconeogenesis. This is a metabolic pathway that generates glucose out of non carbohydrate molecules. Here there are differences between amino acids as well. Some amino acids are able to produce glucose (glucogenic), some produce ketones (ketogenic) and some do both.
Once again, these amino acids are absorbed into the portal circulation and directed towards the liver where excess amino acids get turned into glucose. Since it requires liver processing, insulin is required as a signalling molecule. Since the protein does not raise blood glucose, even though it raises blood insulin, glucagon is also stimulated, as well as incretins that help mitigate this effect and prevent hypoglycemia.
It is a surprise to some, that certain proteins stimulate insulin as much as the refined carbohydrates. Animal proteins tend to have more of an insulin effect than plant proteins. There is a higher risk of diabetes for increasing quartiles of animal protein.
Dietary fat, on the other hand, is metabolized in a completely different manner than both carbs and proteins. Dietary fat is broken down into fatty acids by pancreatic enzymes (lipases) and bile salts. They are then absorbed into the lymphatic system as fat droplets (fat is insoluble in water) called chylomicrons. These do not go into the portal system and do not enter the liver. They empty directly into the bloodstream through the lymphatic circulation and then to the thoracic duct.
This is the reason why dietary fat does not require insulin. There is no further processing or handling, so insulin signaling in the liver is not required for metabolism. This dietary fat can be stored or used for energy. If you were to eat pure fat (say,
Bulletproof coffee), then no glucose or protein is ingested and insulin stays low. The body then simply burns fat.
Burn sugar or burn fat
There are essentially two fuel systems for the body. You can either burn fat, or burn sugar. These two fuel systems are separate and do not interact (see
Randle Cycle for more details). When insulin levels are high, then the body runs on glucose. During that period, there is simply no reason for your body to burn body fat. Why would it? It’s there in case of emergencies, in case there is nothing to eat as a store of calories. It’s like a back-up generator. If you have power in the house, then the generator stays off and none of the fat is used up.
However, if you switch to a low carb, high fat diet, then there is little glucose available to run that fuel system. In this case, the ‘backup generator’ will kick in and start burning fat for fuel. That’s great, because more than anything else, we want to burn fat.
According to the older Carbohydrate-Insulin Hypothesis, carbs are fattening, whereas protein and fat are not. Yet grouping protein and fat together makes no sense because protein metabolism has much more in common with carbohydrate rather than fat metabolism.
The more insulin-centric Hormonal Obesity Theory leaves dietary fat distinct from both carbs and protein. Both agree that refined carbohydrates need to be restricted. However, because excess protein is converted to glucose, it can stop ketosis and weight loss efforts. So here, carbohydrates and excess protein are treated similarly, where fat is distinct. This reflects a far more physiologically accurate picture of metabolism.
So, if you eat a low-carb meal, but eat high protein (protein bars, protein shakes, whey powder etc), then your body will still be burning glucose as it ramps up gluconeogenesis to convert that excess protein to glucose. You are stuck in the ‘Burn Glucose’ fuel system. So
you don’t burn fat.
You want to lose body fat? You gotta burn it off. What keeps you on the ‘Burn Glucose’ side? Insulin. It’s the insulin, stupid! The solution then, is obvious –
low carb, moderate protein, high fat diets."
—
Jason Fung
