Nutritional science: what to believe and what not
Health / / December 19, 2019
Once upon a time study of power was a simple matter. In 1747, a Scottish doctor James Lind (James Lind) decided to find out why so many sailors are ill with scurvy - a disease that leads to exhaustion and anemia, bleeding gums and tooth loss. So Lind gave the first clinical study of 12 patients with scurvy.
Sailors were divided into six groups, each had different treatment. People who ate lemons and oranges, eventually recovered. Irrefutable results, which revealed the cause of the disease, that is, the lack of vitamin C.
Like this solved the power problem in the pre-industrial era. Many major diseases in order of time, such as pellagra, scurvy, anemia, goiter, appearing as a result of a lack in the diet of a given element. Doctors hypothesize and experimented until empirically not found the missing piece of the puzzle in the diet.
Unfortunately, now studying nutrition is not so easy. During the XX century, medicine has learned to cope with the majority of diseases caused by an unbalanced diet. In developed countries, for most people this is not a problem.
Today, the biggest problem was overeating. People consume too many calories and low-quality food, which leads to chronic diseases such as cancer, obesity, diabetes or diseases of the cardiovascular system.
Unlike scurvy, not so easy to deal with these diseases. They do not appear sharply overnight, but develop over the years. And the purchase of a box of oranges from them do not get rid of. Need to study the whole diet and way of life of the patient, to weed out all the risk factors that lead to the disease.
So the science of nutrition has become inaccurate and confusing. There was a sea of conflicting studies, which can be easily detected inaccuracies and weight restrictions. Clutter in this area leads to the fact that advice on nutrition only confusing. Scientists can not agree, tomatoes protect against cancer or provoke it, be useful or harmful red wine and so on. Therefore, journalists writing about nutrition, often sit in a puddle, describing the progress report.
To get an idea of how difficult to study nutrition, Julia Belluz (Julia Belluz) interviewed eight researchers. And that's what they told me.
To find answers to common questions about the power to conduct a randomized trial is pointless
The gold standard of evidence-based medicine - a randomized controlled trial. Scientists are gaining the test, and then randomly distribute them into two groups. One gets the medicine, the other - a placebo.
The idea is that due to random sampling becomes the only significant difference between groups receiving drug. And if the research results vary, it is concluded that the reason the medication (just as Lind calculated that fruits cure scurvy).
The fact is that for the most important questions about nutrition, this approach does not work. Too difficult to assign several different groups dietWhich will be strictly adhered to for a long time to determine which food affects any disease.
Bains Ben Goldacre (Ben Goldacre), physiologist and epidemiology
In a perfect world I would have taken for the study of 1000 newborn infants, divided them into two groups. To one group fed only fresh fruits and vegetables up to the end of life, and the other - bacon and fried chicken. And then be measured in a group often suffered from cancer, heart disease, who would previously grew old and died, who would have been smarter and so on. But it would have to keep them all in prison because there is no other way to make the 500 specific person is not trying anything other than fruits and vegetables.
Wonderful that scientists can not imprison people and force to keep them on a diet. But this means that the current clinical studies are littered and unreliable.
Take, for example, one of the most expensive and extensive research Women's Health Initiative magazine. Women were divided into two groups, one of which is adhered to the normal diet, and the other - a diet low in fat. It was assumed that this test will be fed for several years.
What is the problem? When the researchers collected data, it appears that no one to implement the recommendations. And both groups will eventually eat the same.
Walter Willett (Walter Willett), physiologist, nutritionist at Harvard University
Billions were wasted, and the hypothesis has not been tested.
Rigorous randomized placebo-controlled trials can be carried out in a short time. Some studies of nutritional supplements allow you to organize accommodation tested in the lab for a few days or weeks and monitor everything they eat.
But such studies can not say anything about the effects of long-term diet that you can stick with for decades. All that we can know - cholesterol level fluctuations in the blood, for example. Researchers are only making the assumption that in the long run something for the health.
Researchers have to rely on observational data, which is full of unknown variables
Instead of randomized research scientists have to use data observational studies. They are held for years, they involve a huge number of people who are already fed as necessary to the researchers. Periodically, among them are carrying out inspections, to identify, for example, the development of cancer and diseases of the cardiovascular system.
So scientists learn about the dangers of smoking and the benefits of physical education. But due to lack of control, as in the experiments, this research is not enough accuracy.
Let's say you are going to compare people who for decades consume a lot of red meat, and people who prefer fish. The first problem is that these two groups may differ on other parameters. They even none not distributed randomly. Maybe fans of income above the fish or education is better, maybe they no longer look after themselves. And that some of these factors will have an impact on the results. Maybe meat lovers more likely to smoke.
Researchers may try to control these contextual factors, but keep track of them all is impossible.
Many studies of the diet rely on polls
Many observational (and not only) study relied on survey data. Scientists can not stand for decades over the shoulder of every man and watch what he eats. We have to ask.
There is an obvious problem. You will recall that yesterday ate for lunch? Crumbled nuts in a salad? And then something to eat? And how many grams you eat this week chips?
Most likely, with the necessary accuracy, you will not be able to answer these questions. But a huge number of studies using these data: the people themselves tell us that remember.
When the researchers decided to test the methods of power estimation based on the memories, for the magazine Mayo Clinic Proceedings, Found that these "fundamentally wrong and hopelessly spoiled." Having considered the almost 40-year national study on health and nutritional status of the population, which was based on self-reports of diet, scientists concluded that the claimed amount of calories, which said 67% of women can not match the physiologically objective data about their mass index body.
Maybe it happened because of the fact that all the lies and give the answers that would approve public opinion. Perhaps memory fails. Whatever the reason, researchers from this is not easier. It was necessary to create protocols that take into account some mistakes.
Christopher Gardner (Christopher Gardner)
I need a camera, stomach and intestinal implants, as well as the device in the toilet, which will collect all of your allocation, process them and instantly send information about their full strength.
Christopher Gardner, a researcher at Stanford, said that in some studies it provides participants with nutrition. Or attracted nutritionists who monitor in detail the diet of the test by checking their weight and health status, to confirm the purity of the experiment. He calculates the error of which will be borne in mind when analyzing the results of others.
But researchers dream of better tools, such as sensors, locking chewing and swallowing movements. Or trackers, which will display the movement of the hand from the plate to your mouth.
All different. And the people and products
Though few have problems with data accuracy... Scientists have learned that different bodies react differently to the same food. This is another factor that complicates the study of the influence of diet on health.
In a recent study published in the journal CellIsraeli scientists have observed for 800 participants for a week, constantly collecting data about the level of sugar in the blood, in order to understand what the response in the body causing the same food. each person has an individual reaction, it is suggested that universal recommendations for the composition of the diet bring limited benefits.
Rafael Perez-Escamilla (Rafael Perez-Escamilla), professor of epidemiology and public health at Yale University
It is clear that the influence of diet on health can not be considered only from the point of view of the fact that a person uses. Much depends on how nutrients and other bioactive food components interact with the genes and intestinal microflora of each individual.
We complicate the problem. Foods that look the same, in fact vary in composition of nutrients. Local carrots, grown on the farm, will contain more nutrients than carrots mass production, which lies on the shelves of supermarkets. Hamburger eatery will contain more fat and sugar than with house. Even if people will report that they ate, the difference in the composition of the products will still affect the result.
There is also the problem of a meal replacement. When you begin to use a single product in large quantities, you have to limit the use of something else. So if a person decides to stick to a diet rich in, for example, legumes, it is likely to be eating less red meat and poultry. The question arises, and what affected the performance of more than: beans or giving up meat?
The latter problem is clearly illustrated research included in the fat diet. When the researchers looked at a group of people sitting on a diet low in fat, we found that a lot depends on what to replace fatty foods. Those who began to use fat instead of sugar or simple carbohydrates, resulting in obese and other diseases in the same amount, as well as people who ate a lot of fat.
Conflict of interest - the problem of food research
There is another difficulty. Today, the science of nutrition can not rely on public funding. This creates a vast field for sponsorship by private companies. Simply put, the food and beverage producers pay a huge amount of research - sometimes the results are uncertain. And the legislative sphere power is not as tightly regulated as medicine.
Nestle Marion (Marion Nestle)
many studies sponsored by manufacturers that professionals and consumers may question even the basic principles of healthy eating.
paid-for research incline the results of which are beneficial to sponsors. For example, of the 76 sponsored research conducted from March to October 2015, 70 did conclusionsWhich it was necessary for food producers.
"Basically, independent research found a link between sweet drinks and poor health, and those who paid for the conduct of the producers of soda, do not find" - says Nestle.
In spite of everything, the science of nutrition is alive
Difficulties studying nutrition create a feeling that learning something unambiguous about the impact of diet on health in general is unreal. But this is not the case. Researchers have for years enjoyed all these imperfect tools. A slow and careful approach is justified.
Frank Hu (Frank B. Hu), a professor of public health and nutrition, Harvard University
Without these studies, we would have never known that a lack of folic acid during pregnancy leads to the development of fetal malformations. We would not know that trans fats negatively affect the heart. We would not know that soda in large amounts increases the risk of diabetes and fatty liver disease.
The researchers described how they determine which data to trust. In their opinion, it is necessary to evaluate all available studies on the same issue, rather than individual reports.
They also recommend to look at the different types of studies that are devoted to a single subject: clinical research, observations, laboratory studies. Different works with different inputs, different methods, which lead to the same results - it is objectively a good indicator that between diet and changes in the body there is a connection.
It is necessary to pay attention to the source of funding for research. Independent conducted on public money and public funds, they have more confidence, particularly because the plan is less than limitations of the study.
Good researchers never say found superfood, and advised not to completely abandon of a product, do not make bold statements about the effects of the use of a specific type of fruit or meat, limited to the assumption that a particular diet can be helpful.
These tips will reflect the consensus groups researchers recently discussed the issues of nutrition and health. Here are the conclusions of their meeting:
Healthy diet composed of a large number of fruits, vegetables, whole grains, seafood, legumes, nuts, low fat; also need to observe moderation in the consumption of alcohol, red meat and processed meat products. And then there is less sugar and processed grains. Not necessarily completely abandon any food group or adhere to a strict diet in order to achieve a positive effect. You can combine products in many different ways, making a balanced diet. The diet should take into account individual needs, preferences and cultural traditions.
Allegations that cabbage or glutenFor example, kill humanity, can not be called the voice of science. Because, as we understood, the science simply can not prove anything.