When do you know you have eaten enough?

Our bodies are very sophisticated machines. Through biochemistry, metabolism and physiology, they have developed an amazing ability to regulate themselves. For instance, glycaemia level and blood pH are monitored constantly by sensors that in turn send information to organs and trigger them to get into action whenever is needed. Our brains know only one fuel with which they can function: glucose. Any slight deviation in glycaemia or blood pH that lasts too long can lead to brain damage and even death. Brain sensors can tell the body when it is running low on fuel and the message as we know it is to feel hungry. Brain sensors can also tell us when the fuel tank is full and that is the feeling of being “full” or also known as satiety.

To indicate satiety, our body has two information systems. The brain sensors are only one of them. They function on the blood chemical composition, but of course for nutrients to get into the blood stream and have glycaemia and blood pH back to the proper levels, it takes time. The food has to be processed through the stomach and then transit in the intestine where the nutrients are absorbed and enter the blood stream. The other feedback system is not about biochemistry but more of a mechanical one. There is a nervous connection that goes from the stomach to the brain. When the stomach is being filled, the stomach wall stretches and when the stomach has been filled at capacity, the nerve sends a direct and rather immediate message to the brain to let it know that it is full and should no longer receive any more food. The brain read this message as satiety and the feeling of hunger disappears. The combination of these two systems is great but it has a flaw, though, as it had not been prepared for modern eating habits. It is possible that the flaw was never a cause of problems in the past because the diets of then would not act on the flaw (for background read my previous article Lifestyles have changed but our biology has not). So what is the weakness of the satiety feedback? I see two main reasons: calorie density and pace of meals.

When a person eats a high-calorie meal, s/he ingests a high level of calories in every bite. If the person starts with food rich in fat (9 calories per gram), carbs or protein (4 calorie per gram), s/he usually will get them from foods that do not contain too much water, so the calories are not all that diluted. Opposite to this, if the person starts a meal with a salad or a soup, such dishes are rich in water and in fiber, too. Fresh veggies will contain at least 90% water, and so could be soup depending on how much water you put in it of course.

The pace of the meal or, in other words, fast food versus slow food plays a role in the sense of how much time it takes to ingest all the calories. Remember, it takes time for nutrients to be absorbed and enter the blood stream. The slower you eat, the more time you allow that process to happen before ingesting more calories. That way, you do not fill the tank too fast. But if you eat fast, you can ingest more calories that you need before the chemical satiety feedback system reaches you brain. You brain think that you are not full yet, meaning that you have not ingested all the calories you need, while you actually have. If you eat fast but you eat low-calorie density food, it might not be a problem because you still may not have exceeded your calorie intake when the mechanical feedback through the nerve kicks in. On the opposite, if you eat high-calorie density food fast, you can be almost sure that before your stomach can let the brain know that you have eaten enough, you will have ingested too many calories. The reason is simple: high-calorie density foods take less volume than high-density calorie foods. One pound of feathers has a much larger volume than one pound of lead, same idea. Since the stomach-to-brain connection works on the stretching of the stomach, the stomach will allow a higher volume of high-calorie density food to enter before sending its message to the brain, thus allow you to eat more calories than you need to. And if you combine high-calorie density with fast eating, you will get ahead of the biochemical feedback as well. In the category high-calorie density that do not fill the stomach, do not forget to include soft drinks. Just like as indicated in that same previous article, all the calories that you do not burn will be stored as body fat. This explains a lot of why wrong eating/drinking habits can result in overweight and obesity. Although they are not necessarily the only contributors, but they certainly do contribute to the problem.

This leads me to a theory that some people have about why the French who eat their traditional diet of two large meals a day are not particularly fat. The traditional French diet (I would include all the Southern European diet in this, too) consists of long meals, usually at least an hour at the table, and have several courses, as you could see on the school canteen menu in my previous article. The first course is often a salad or a soup, which is low-calorie density. It starts filling and stretching the stomach, but the person does not ingest a lot of calories by then. Then comes the main course. Because the person is already a bit full, s/he does not feel the need for a huge portion, which means that the amount of calories in the main course will not be that high. The meal ends with a dessert, which can have a high-calorie density, but since the person already filled the stomach with the previous two courses, the dessert size is not that big. The calorie density pattern is not the only characteristic of a traditional French meal. The fact that the lunch and dinner take a long time, there is hardly any lag between the food intake and the biochemical satiety feedback. A traditional French meal is actually a very harmonious process between a variety of foods and letting the body carry out its physiology as it is intended to be.

© Christophe Pelletier – The Happy Future Group Consulting Ltd.

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