We all want to know what is the best diet for humans. Many of us actually have an opinion about this question. Some believe that a low fat, plant-based diet is the best. Others, that a low-carb diet, rich in protein and animal fat, is the best. Others have opinions on how much sugar we should eat, or how much salt, cholesterol, saturated fat, eggs or dairy products we should have in our diet.
But the question of what the best diet is, is a scientific one, so there should be no room for opinions or beliefs. The truth is that the best diet does exist. Now, you might think it’s because people don’t listen to what we tell them. But in fact, that’s not true, people actually generally do follow dietary guidelines. But according to the Center for Disease Control, if you live in the United States, there’s over a 70 percent chance that you’re either overweight, diabetic or have non-alcoholic fatty-liver disease. And there’s overwhelming evidence that diet and lifestyle are major drivers of these conditions. So why is it that after so much research, we still don’t have an answer to the seemingly simple question of what is the best diet for humans?
Raditional thinking suggests that the effectiveness of a diet is solely dependent on the food it comprises. However, emerging research indicates that this may not be the complete picture. Consider the role of individual differences such as genetics, lifestyle, and gut bacteria. These factors can significantly influence how we respond to food. Could these differences be the reason why certain diets work for some people but not for others?
To take a scientific approach, is important to take a metric be relevant for weight management and diet-related disease, but also easily to measure. And this led to focus on changes in blood glucose levels after a meal. We call this a “meal glucose response” Why is it important?
High glucose levels after a meal can lead to hunger and weight gain. The body digests carbohydrates into simple sugars and releases them into the bloodstream. Then Insulin helps cells to convert glucose for energy, but it also signals the body to convert excess sugar into fat and store it, gaining weight. Fast glucose flow can cause too much insulin release, lowering glucose levels and making us feel hungry. Meal glucose responses are crucial for health as they are risk factors for obesity, diabetes, cardiovascular disease, and other metabolic disorders.
In the study [1] scientists have managed to convince 1,000 healthy people to connected them to small glucose sensors and tracked their glucose levels continuously for an entire week.
So what did we find?
- More carbohydrates in the meal generally increase the response. This is not so surprising.
- Another, perhaps more surprising, trend is that more fat in the meal generally decreased the response.
But the key finding of the study – for every trend they found, there were many people who were very different from it. Basically, when the same person ate the same meal on different days, the response was very similar. But when different people ate the same meal, the response was very different. For example, white bread induced almost no effect on the blood sugar levels of some people, but in others, it induced huge spikes.
Some people even had opposite responses. For example, some people spiked for ice cream but not for rice. But then others spiked for rice and not for ice cream. In fact, more people spiked for rice than for ice cream. Clinical dieticians, of course they relie on general dietary guidelines, and so one of the first things that tehy tell to many newly diagnosed pre-diabetics is to stop eating foods such as ice cream and instead eat more complex carbohydrates such as brown rice. So, in some patients not only this dietary advice does not help, but actually makes the situaion worse.
So responses to food are personal, and that diets that maintain normal blood glucose levels must therefore be personally tailored to the individual.
The best diet for humans does not exist.
So what’s the take-home message from all of this? Well, based on the glucose responses variability the conclusion is that there is no single best diet for humans because we are all too different. It also means that if a certain diet hasn’t worked for you, then maybe it was the wrong diet for you. Your dietary failures may not be your fault. Your diet may have failed simply because it did not take information about you as an individual into account.
References
1. Zeevi, D., Korem, T., Zmora, N., Israeli, D., Rothschild, D., Weinberger, A., Ben-Yacov, O., Lador, D., Avnit-Sagi, T., Lotan-Pompan, M. and Suez, J., 2015. Personalized nutrition by prediction of glycemic responses. Cell, 163(5), pp.1079-1094. https://www.cell.com/cell/pdf/S0092-8674(15)01481-6.pdf