The Idea Behind The Perfect Fit Diet should come as no surprise to doctors. We already know that when it comes to treating disease, one size does not fit all. Over the past 20 years, science has made dramatic discoveries in the areas of genetics and physiology, in the way even the smallest cells in the body interact with different medications and other therapies. Using this ever-expanding knowledge base, doctors hope some day to be able to devise an individualized treatment regime based on a patient’s medical profile, family history and what we know about their genetics to control chronic diseases.
Take high blood pressure, for example. In just the past 20 years, doctors have enjoyed the ability to prescribe several drugs that work very well at lowering high blood pressure. Only recently, though, have studies confirmed what doctors sort of knew in their gut: these medicines have different effects on different people. In 1993, The New England Journal of Medicine published a study that compared the effects of six classes of high blood pressure medicines on a group of tens of thousands of former soldiers. Half the sample were white; half were black. This study supported what had been shown in several smaller studies – that blacks responded better than whites to a class of medicines known as calcium channel blockers and worse than whites to another class of medicines known as ACE inhibitors. Why that should be the case is still being investigated. That it is true has been accepted and shapes medical decision making thousands, perhaps millions, of times a day.
More recently, science has witnessed the birth of an entire field, known as pharmacokinetics, dedicated to the investigation of the inherited mechanisms that determine the responses to medicines that are used to treat everything from depression to cancer. This discipline grew from the widespread recognition that different patients respond differently to the same medications. For example, it has long been known that, while codeine is a wonderful pain reliever for most of us, for about 6 per cent of the population it offers no relief, no benefit.
It just doesn’t work. Why? Because in order to work as a painkiller, codeine has to be broken down into its morphine base. Six to 7 per cent of the population is born without the machinery to perform this chemical transformation. This tiny genetic difference has no other effect except to make a good painkiller ineffective. Here’s another example, perhaps a little closer to home. Researchers in Canada wanted to see if obesity had a genetic component in addition to the environmental aspect already well-recognized.
They found a group of twins and for several weeks fed these people 1,000 calories more than they normally ate. Each of the identical twins gained about the same amount of weight. Different twin sets, however, gained very different amounts ranging from 4.5 to 18kg (10 to 4Otb), proving that your genes strongly influence how you gain weight. Same ‘therapy’ (overeating by 1,000 calories a day) very different results.
The same is turning out to be true for the treatment of obesity as well. For example, there is a segment of the population that processes carbohydrates differently from most of us. These people are born with a tendency to become resistant to the effects of insulin. Because of that difference, when they eat a diet low in fat and high in carbohydrates a diet designed to lower cholesterol they develop high cholesterol instead. Thus, the most popular diet among doctors and dietitians today is not the healthiest diet for those with this abnormality known as metabolic syndrome. Again, the same therapy will cause a very different effect in some of us. It is likely that there are other differences between people and the way they process certain foods. For instance, there is good evidence that small dissimilarities in several genes make dramatic differences in the ways some people respond to the amount and type of fat in their diets. These mechanisms are still not well understood but are the target of much investigation right now.
There are variations not only in the way we process food but also in what causes us to feel full and stop eating. What makes us stop eating is actually a very complicated process and is probably controlled in many ways. However, it seems clear that when it comes to feeling that we’ve ‘had enough’, different people respond to different cues. We humans (as well as other species) have what is called sensory- specific satiety. What that means is that the enjoyment of any given flavor or texture begins to decrease as more of that food is eaten. But that can happen even while the appetite for other flavors or textures remains unabated.
This is why we can feel full after a big meal of meat and potatoes and still find room for dessert. The appetite for sweets was untouched by the meal, and while you may or may not crave them, the sight or thought of them will appeal to your mouth even if your stomach is ‘full’. This is thought to be part of the biological drive that encourages us to eat a variety of foods. Genetically speaking, this trait comes in handy on the savannahs of Africa if you’re an Australopithecus primate trying to evolve into a human being. If you’re plopped down in front of the TV, this trait has a whole other impact.
This form of feeling satisfied actually takes place in the mouth. We know this because researchers have done experiments where a food was eaten but wasn’t allowed to reach the stomach. Research subjects were instructed to treat test foods the way an oenophile might treat wines at a tasting. They were to put the food in their mouths, savor it, then spit it out. The satiety for the flavor remained, even if the eater wasn’t any more full.
Other research shows that volume of food is an important cue of satiety. In one experiment, 20 young men were given four different drinks before four meals. The drinks had the same total number of calories contained in different amounts of fluid. They drank this before eating lunch, and then the amount that each of the men ate at lunch was carefully monitored. The more fluid the men drank, the less they ate at lunch, even though the amount of calories in the drinks were the same. So volume of food is an important factor for many people. Another powerful satiety cue for many people is the richness of a food that is, how much fat and protein it contains. These foods trigger the release of specific digestive enzymes that not only work to break down these foods but also travel to the brain to report that you have eaten them.
It seems clear that different people have different responses to these various satiety cues. Two studies recently published in The New England Journal of Medicine identified a genetic variant in a small percentage of obese children, which made them produce less of a brain hormone known to cause a feeling of fullness. The clear implication is that these children may be obese Simply because they never really feel
full or satisfied by a meal. And there is evidence that, particularly in the overweight and obese, cues to stop eating can be overwhelmed by other feelings and sensations. So it may well be that once you start gaining weight, it becomes easier to gain more, because the body’s usual mechanisms for controlling diet are misfiring.
Obviously, if you are trying to reduce the amount of food you eat, then choosing foods that will provide you with the loudest and clearest cues that you’ve had enough will be an important way to start any good diet. Forcing you to eat foods that don’t relay this key Signal to the brain regardless of how good they may be for you is going to be frustrating and undermine the ‘willpower’ of the dieter.
When you are selecting a diet, you will want one that gives you every possible advantage in staying on it: one that allows you to eat the foods you like and avoid the foods you don’t like; one that takes advantage of whichever form of satiety speaks to your body best; one that is best for your body and your health. Can we predict who can stay on a diet and who can’t? Anyone who has tried to diet knows that it’s not about motivation. The key to being able to stay on a diet is how well that diet fits you as an individual.
Related posts:
