Diets: more than streaks, tests

Etxebeste Aduriz, Egoitz

Elhuyar Zientzia

It is increasingly evident that diet has a great impact on health. And it is increasingly evident that many of the very common evils in our society are directly related to diet. Therefore, it is essential to be clear what a healthy diet is. There are different views and disagreements, but also important consensus.
Ed. A. Vlasopva/

They are diets that become fashionable, they are different trends, they are changing messages that come from experts, for those who want to follow a healthy diet it is not always easy to know what is the right way and choose between the different existing trends. The journal Science brought together several experts to analyze different points of view, to review what the existing scientific evidence says so far and underline consensus. This work was published in an article published last November.

The first thing they stress is that, although for many years the forces have been put in fat reduction, this has not meant health benefits. They have been based on American data. There, 42% of the calories consumed daily in the 1970s came from fats, a proportion that currently reaches 34%. However, obesity and diabetes have increased considerably and, for the first time since the influenza pandemic 100 years ago, life expectancy has decreased.

This seems to be due to processed carbohydrates. In fact, fat reduction has led to a considerable increase in consumption of processed carbohydrates. And studies in recent years are showing that these carbohydrates are not beneficial to health. However, “here we still consume too much fat”, explains Mª Puy Portillo Baquedano, professor of the research group Nutrition and Obesity of the UPV/EHU and president of the Spanish Nutrition Association. “What we recommend today is that fat present between 30 and 35% of calories, and we are well above: 35-42%. We know that this food model is not adequate, since an excess of fat contributes to the development of many pathologies”.

Excess fat

“When we eat too much fat, we usually take too many calories,” adds Portillo. In fact, fats have twice as many calories per gram of carbohydrates and proteins (9 kcal/g and 4 kcal/g the other two), have greater palatability and lower saturation. In an experiment conducted last year, with 29 diets of different proportions of macronutrients to mice, it was observed that low-fat diets only caused excessive calorie consumption and fattening. In addition, they observed that high-fat diets influenced the brain reward system, increasing the expression of serotonin receptors and dopamine and opioid system genes.

“Taking more calories than needed leads to overweight, then obesity. And obesity can produce insulin resistance and then diabetes,” explains Portillo.

On the other hand, “if we eat too much fat, it’s normal for an important part of that fat to be saturated fat,” adds Portillo. “Unsaturated fat is healthier, but when you eat a lot of fat it is very difficult for everything to be unsaturated. And excess saturated fat can lead to the development of other diseases such as dyslipidemias (high cholesterol LDL, high triglycerides, low cholesterol HDL) and cardiovascular disease.”

Mª Puy Portillo Baquedano. Professor of the research group Nutrition and Obesity of the UPV and president of the Spanish Nutrition Association

In fact, in addition to calories, high fat intake can have very different physiological effects. For example, it increases the activity of several factors that cause inflammatory processes. And many of the most common evils today are based on inflammatory processes such as obesity, diabetes or arteriosclerosis.

On the other hand, fat causes an increase in the synthesis of bile acids in the liver, which causes the accumulation of secondary bile acids in the colon. This increases the risk of developing tumors. And excess fat also influences DNA methylation. That is, it produces epigenetic changes.

Given all the physiological effects of fats, it is quite clear that excess fat is harmful to health. But another clear conclusion drawn by the authors of the Science article is that, despite the reduction of fats, the quality of the carbohydrates that replace them is very important. In fact, the effect of refined carbohydrates can be as harmful as an excess of fat.

Portillo agrees: “Processed foods have many refined sugars; and if you take a lot of refined sugar, again, it is normal to eat too many calories and get fat, and all that comes, obesity...” In addition, processed carbohydrates are fed little, causing sudden rises and falls of sugar and insulin, resulting in hunger, inflammations, insulin resistance and dyslipidemias.

Perhaps because of the damage caused by the increase of poor quality carbohydrates, or by diets with a lot of fat, there are more and more followers. At this time, in the Amazon threshold weight loss books, four of the top five sold refer to ketogenic diets based on eating most of the calories in the diet (70% or more) of fats.

Some scientific goal studies show that high-fat diets can be somewhat more effective than low-fat diets for weight loss, especially in people with insulin resistance. And there are studies that suggest that these diets can be very effective in controlling diabetes. In addition, it has been detected that diets with high fat content can improve the levels of some markers of cardiovascular diseases (triglycerides, HDL cholesterol, blood pressure...).

Diet in treatment

“To treat metabolic syndrome there is no adequate diet for all cases,” explains Portillo. “It is not the same to treat a person with diabetes as with a high level of triglycerides, that with diabetes and obesity or with all three. Those who have a high level of triglycerides may have more monounsaturated fat and less carbohydrates, but those who have triglycerides well, perhaps the other way around.”

Obesity and diet-related diseases are becoming more common among children, among other things because they consume a lot of foods and drinks high in refined sugars. ED. : Kwandrai.c/

Equal to lose weight. “A person, according to their metabolic characteristics, can better respond to a diet with more fat and less carbohydrates, or vice versa. And some get much more exercise than dietary treatment. That is why we are increasingly going to customize diets. But always within a few limits.”

The aforementioned ketogenic diets are excluded from these limitations. Carbohydrates are drastically reduced, and almost all calories are taken mainly from fats and other proteins. “It is a very unbalanced diet, extremely extreme, with many problems from a dietary and metabolic point of view,” explains Portillo. “It’s true that some people with a very controlled ketogenic diet lose a lot of weight. At the hospital we are seeing good results with some patients. But they are always used as shock treatment and in the short term. Such a long diet is unthinkable.”

Portillo wants to make it clear: “We have to differentiate very well what is a diet that can be for a certain treatment and what is a customary diet to be healthy. Ketogenic should be understood only as treatment and always under medical control.”

It is called ketogenic due to the formation of ketone bodies. These bodies cross the blood-brain barrier and reach the brain. “From a certain level they are dangerous. That's why you have to control it very well. It is not convenient for anyone to make these diets on their own, as they will not control the level of ketone bodies. You will lose weight, but you will have many undesirable effects.”

This conclusion is also reached in the Science article, which seems that ketogenic diets can serve for specific cases where abnormal carbohydrate metabolism is the most common. But they stress that better research is needed.

Need for research

It also highlights that there is much to research on the impact of different types of fats on health. Portillo agrees and gives an example: “Until recently we had among those who should avoid or reduce milk fat, because it is saturated fat. However, studies in recent years are showing that, despite being saturated, the influence of dairy fat is not the same as that of other saturated fats, and can even be beneficial.”

Ed. Kwangmozza/

The researchers highlight the need to conduct quality research on the impact of diet on health and denounce the low investment in it, taking into account the cost of treating food-related diseases. “We would have to invest more in research and prevention in public health actions, first because it would improve people’s health, but, on the other hand, it would be better economically,” says Portillo.

If nothing changes, the cost of treatment will increase. “On the one hand, because we live more, even with the hangover, and on the other, because diseases start more and more early. A few years ago there could be some child with obesity, but it was almost unthinkable that children had type II diabetes, or had hypertension, and I never heard hepatic steatosis. And now there are 10-year-old children with these diseases. It’s terrible,” says Portillo. “If you invest more in research and prevention, in some generations the situation would change, but the problem is that it is a long-term issue and politicians want short-term results.”

Clear agreements

In fact, although there are still many details about the health impact of the diet to be investigated and resolved, almost all experts agree that the general points for a healthy diet are quite clear. In fat/carbohydrate ratio, a relatively wide range could be healthy, especially in food quality. It is recommended to replace saturated fats with unsaturated fats and processed carbohydrates (refined flours, potato derivatives and free sugars) with unprocessed (vegetables, fruit, legumes and whole grains).

Portillo defends the Mediterranean diet. “The Mediterranean diet is scientifically proven. Between vegetables and fruits we should take five famous pieces a day. They have few calories, a lot of fiber, many vitamins and minerals and many other compounds that are very beneficial to health, such as polyphenols. Cereals, preferably whole. Legumes are also very interesting, but without sacraments and not in large dishes, because they have many calories”.

“Fish more than meat and, when eating meat, choose low-fat pieces. We eat too much meat, many think that meat is still necessary, but not. Of great interest they help control fat, blood sugar and lipids, among others. And, of course, olive oil.”

The aspects to avoid are also clear: “sausages only occasionally, for their high content in saturated fat, and sweets and drinks and foods with added sugars, only for exceptions. Simple sugars are not necessary at all and are harmful. We have all the ultra-processed ones that fill the Superr shelves.”

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