Find your "special" food

Spector is a genetics scholar. For ten years, he has eaten the same food for lunch every day: a tuna sweet corn brown bread sandwich, plus a banana. Like most people, he thinks these foods are very healthy. But he found that his blood sugar and blood lipid levels always soared after such a lunch. High blood sugar and high blood lipids are risk factors for diseases such as diabetes, cardiovascular disease and obesity.

Although a tuna sandwich may not seem healthy to Spector, it may be very healthy to someone else. Other foods that are generally considered unhealthy, such as ice cream, vary from person to person. Scientists have found that the body's metabolic response to the same food is highly individual. In theory, everyone's diet should be different if they want to be healthy.

Glycemic response varies from person to person

In 2014, an Israeli research team conducted a study to explore whether artificial sweeteners used to replace traditional sugars and help alleviate obesity and diabetes would actually worsen the condition. They gave saccharin (an artificial sweetener) to healthy volunteers, and the results were unexpected: the blood sugar levels of the volunteers after consuming saccharin showed a high degree of individual variation - some of them had a significant rise in blood sugar, some had a normal increase, and some had almost no increase.

There are two points that puzzle the researchers: first, artificial sweeteners themselves do not contain calories and theoretically will not cause a rise in human blood sugar; second, the degree of blood sugar surge should not vary so much among different individuals - in theory, after eating the same amount of the same food, although there are differences between individuals, the level of blood sugar rise should be roughly the same.

"One man's meat is another man's poison". The glycemic index (GI) can explain the above two questions. The glycemic index is an indicator that measures the effect of food on blood sugar levels. Foods with a high glycemic index will be quickly digested and absorbed, causing a sharp rise in blood sugar. In fact, it is not very meaningful to study the effect of a certain food on the blood sugar levels of different individuals, because it is impossible to draw a universal conclusion. The glycemic index describes the average blood sugar increase level of different individuals after eating the same food, so it is universal.

Scientists conducted an experiment to test the blood sugar fluctuations of healthy volunteers using white bread (white bread is generally considered unhealthy because of its high glycemic index of about 75). Scientists thought that the blood sugar-raising effect of white bread would be significant. However, after eating white bread, some people's blood sugar levels hardly surged, while others surged to diabetic levels. But no matter how different the white bread caused the blood sugar levels of different volunteers to rise, their average level of increase tended to a value, which was the glycemic index of white bread.

This phenomenon breaks people's traditional understanding of food. In other words, there is no "perfect" food, that is, no matter who eats it, blood sugar will not soar. Moreover, because different people may have completely different blood sugar responses to the same food, this food can be said to be "one man's honey, another man's poison." Therefore, instead of evaluating whether a certain food is healthy, it is better to evaluate a person's blood sugar response to the food: if blood sugar soars after eating, then the food is unhealthy for this person.

In another study involving 800 volunteers, researchers integrated various personal information of volunteers, such as age, gender, lifestyle and medical history, and calculated their height-weight index and waist-hip ratio. Finally, they collected stool samples from each volunteer to analyze their intestinal microorganisms. Then, the researchers monitored the blood sugar levels of the volunteers for a week and recorded their meals (meal time and type and quantity of food, with more than 52,000 records), sleep conditions and daily activity patterns. The results were consistent with what the researchers expected: even after eating the same food, the 800 volunteers still had very large individual differences in post-meal blood sugar levels. Subsequently, the researchers found that the factors most closely related to the human body's blood sugar response are individual biological characteristics, especially the composition of microorganisms in the body. This means that with just a few biometric data, a low-glycemic index diet can be customized for anyone.

To further prove this conclusion, the researchers recruited 26 volunteers who may have prediabetes (i.e., they have impaired glucose metabolism but do not meet the diagnostic criteria for type 2 diabetes) and customized two sets of personalized diets for each of them based on the composition of their microorganisms. The first set caused blood sugar to soar, while the second set did not. After a week, the researchers found that the first set of diets made the volunteers' blood sugar response more intense, while the second set improved the blood sugar response. It should be pointed out that unlike the diet previously recommended for patients with prediabetes (such as coarse grains, etc.), the second set of diets also contains some foods that are generally considered "unhealthy" (such as chocolate and ice cream, etc.).

Tailor-made meal plans Spector recently led a study on "Individual Responses to Dietary Ingredients", which focused on the level of triglycerides (a type of fat) in the blood after a meal. 1,002 volunteers participated. The results showed that after eating the same food, their blood triglycerides all showed different levels of increase. Some volunteers' triglyceride levels did not increase much, some quickly dropped to a stable state after rising, and others continued to rise for several hours. In addition, among the 1,002 volunteers, there were 86 pairs of twins with identical gene sequences, but each pair of twins had different abilities to metabolize food, indicating that genes had little effect on food metabolism. Spector concluded that the fluctuations in triglycerides and blood sugar levels after meals in different individuals were highly individual, but the surges in blood sugar and triglycerides did not occur synchronously.

Before the study began, Spector measured the volunteers' age, gender, height, weight, blood pressure, fasting metabolic level, biological rhythm, gene sequence and microorganisms in the body, and recorded their meal times, diet composition, sleep and exercise during the experiment. The above information can be used to predict the individual's metabolic response level to any kind of food. For specific metabolic indicators, triglycerides have an accuracy rate of 77%. Although the results are not precise enough, it is much more reliable to formulate a dietary plan based on this than to recommend "absolutely healthy" foods to everyone.

Other studies have found that analyzing metabolites in a person's urine can also infer their metabolic level. Therefore, it is foreseeable that in the near future, people only need to conduct a few simple tests, such as blood and urine sample tests, and nutritionists can develop targeted dietary plans for them.

However, we should not go to extremes. We still need to roughly follow the widely recognized healthy diet guidelines, such as ensuring dietary diversity, consuming more fruits and vegetables rich in dietary fiber, consuming appropriate amounts of fat, and limiting the intake of processed foods. A personalized diet under this premise is a healthy diet suitable for everyone.