Why do diets work for some people and not for others? It is a question that causes a food industry of several billions a year to continue to resonate for decades, but a new groundbreaking study has finally discovered the answer.
It suggests that there is a big mistake in all those one-size-fits-all guidelines for cutting fat, carbohydrates, or calories that we've been trying to follow for years. They are doomed to fail because they are based on the & # 39; average person & # 39; – and nobody is average.
The fact is that different foods affect people differently in terms of what happens to the levels of sugar and fat in their blood, giving them a greater (or lower) risk of weight gain, heart disease, type 2 diabetes and other serious conditions.
Food labels that tell you how much fat or sugar there is in a food can therefore be largely meaningless for what happens in your body.
Shocked: identical twin Kinga and Kata discovered that their bodies reacted differently to food
That's the far-reaching suggestion of the findings – which are only revealed in today's Mail – of a £ 21 million nutrition study with a collaboration between King & # 39; s College London, and Massachusetts General Hospital and Stanford University in the US
Called Predict 1, the research is led by Tim Spector, professor of genetic epidemiology at King & # 39; s and also a specialist in nutrition and the microbiome (and in the top 1% of scientists in the world whose work is cited by other researchers – a sign of how influential they are).
The first set of results, published today and to be published in the American Journal of Human Nutrition, comes from the most detailed research ever conducted into the direct effects that different foods have on people.
A REVOLUTION IN DIET RULES
it turns upside down some of the shibboleths of nutritional thinking: & # 39; For example, our findings suggest that calorie intake is a vastly overrated measure of weight gain & # 39 ;, Professor Spector told Good Health. & # 39; It is practically not practical because people react differently to foods with the same number of calories. & # 39;
The researchers themselves were surprised at what they learned about how carbohydrates and fats affect us differently.
& # 39; This was the finding that gave me the biggest surprise & # 39 ;, says Dr. Sarah Berry, associate professor of food sciences, also at King & # 39; s College in London. & # 39; It means that the food labels on all packaged foods that contain the amount of carbohydrates and fats are useless. The research found that "macronutrients" (sugar, fat and protein) explained less than 30 percent of the response to food. "
You are what you eat? Kinga discovered that different foods affect people differently in terms of what happens to the levels of sugar and fat in their blood
This could help explain the general finding that some people can seem to see all the donuts they want without getting fat – while others just have to look at a cookie to stack on the pounds.
The Predict 1 study was based on 1,100 participants who were mainly identical twins. This is especially important because it has discovered that individual responses to the same food are unique, meaning that genes cannot explain the different responses to food – like the people who rarely put weight on whatever they eat.
Because twins are genetically identical, those differences must be due to something else.
So what makes the difference? This was the other big surprise of the study. The results show that lifestyle factors, such as how well you sleep or when you exercise, can influence your response to food.
& # 39; Specific lifestyle factors have never been part of dietary advice, but this research suggests that they can make a big difference to the effect of foods & # 39 ;, Dr. Berry explains.
This means that your body's response to food can be improved by changing lifestyle factors such as sleep quality, or even the time you eat your meals.
How did the researchers discover all this dramatic evidence? It concerned every participant who performed detailed measurements at a clinic at St Thomas & # 39; Hospital in London, where they were intensively tested all day.
After a night of fasting, they were given a standard breakfast – white or rye bread with a spread based on vegetable fats – or pasta or rice. For lunch there were a few choices such as spaghetti Bolognese or eggs and fries.
Sweet tooth: research participant Kata discovered that her body processed sugar differently compared to her identical twin sister, despite their shared genetic background
The study participants each wore a 24-hour monitor on their arm, which monitored changes in blood glucose levels. Blood tests were also given every few hours to accommodate changes in fat levels, as well as record levels of metabolites, substances that may reveal details such as liver function and chemicals in the brain, including serotonin.
There was also a series of other recordings. The body fat, muscle mass, insulin levels and markers of inflammation were also monitored during the day. Stool tests were used to check the number of intestinal bacterial strains, and questionnaires were given for meal times and exercise habits. The participants then went home and tested themselves daily for two weeks. They still ate the standard breakfast and the more varied meals. The glucose monitoring continued and during the first four days they had to take blood tests three times a day.
& # 39; This showed that twins eating the same meals can have very different reactions & # 39 ;, says Dr. Berry. & # 39; One could have ten times as much glucose or fat in their blood after the meal as the others, increasing the risk of weight gain or heart disease. & # 39;
ARE BROWNIES YOUR NEMESIS?
There is more: for example, one twin would not show any change in blood sugar levels if she were to train after a carbohydrate-rich meal, while the other twin's blood sugar levels would rise after the same meal if they had not slept well.
The number of strains of bacteria in their gut also influenced how they responded to food.
Take the example of the 35-year-old identical twin Kinga and Kata Varnai, from North London, who participated in the study. Kinga works in clinical informatics for a NHS trust relationship and helps in the effective collection and use of data. Kata is a project manager and organizes training courses for healthcare professionals.
The same difference: when they were given a large brownie, Kinga's blood sugar levels rose as you would expect, but Kata remained flat – proving that individual biology plays a major role
They eat wisely, with lots of whole food and practice regularly. They have been the same weight for ten years and have no chronic conditions. So, health paragons? That is certainly what they thought until a few months ago when they participated in the trial.
The first day they started with a breakfast with white bread – instead of their usual porridge with nuts and seeds – and the controls showed how very different their bodies reacted.
Kata's glucose level changed little after white bread or pasta or rice, while Kinga climbed. But when they had breakfast on another day with rye bread, their answers turned around.
This time it was Kata & # 39; s glucose that rose while Kinga remained stable. & # 39; That was a disappointment & # 39 ;, Kata admits. & # 39; I have always felt that rye was good for me. & # 39;
Despite their overall good health, a number of problem areas came to light.
One of the tests was on their gut flora – research has shown that there are more types of bacteria in your gut, the better it is to process food and nutrients.
Both Kata and Kinga had a & # 39; low average & # 39; number of tribes, but Kata had more than Kinga. This could be the reason for Kata's ability to process carbohydrates better, says Professor Spector.
When they got a big brownie, Kinga & # 39; s blood sugar shot up, as you'd expect, but Kata stayed flat.
According to Professor Spector & # 39; we know that poor levels of intestinal bacteria increase the risk of weight gain and heart disease: we cannot yet say that certain somewhat higher Kata & # 39; s hair protected, but it is possible & # 39 ;.
The data from all these careful measurements are still being analyzed (not least to see how lifestyle factors such as exercise and the intestinal flora all fit together, and why they have the effects they do). But the findings are already set to change dietary advice.
As well as suggesting that the food labels showing the calorie, sugar and fat levels of foods are useless, the traditional advice about when to eat breakfast can also bite the dust.
DIET MUST BE PERSONALIZED
The conventional idea is that breakfast is better digested than other meals, which may be true for some people, but not for everyone.
Some twins – about a third – felt more comfortable later in the day and ate breakfast; their results showed that this improved their fat and sugar levels.
& # 39; Individual variation will be much more taken into account & # 39 ;, says Professor Spector.
This is a study that & # 39; the way nutritional research is done & # 39; can change & # 39 ;, Dr. Berry adds. & # 39; There is so much disagreement about healthy eating because nutrition research is incorrect.
Tailored: the idea is now that we all need personal nutritional advice – once you know how your own body reacts to different types of food, you can make changes to avoid some and use others
& # 39; Usually it depends on answers to food questionnaires that ask: did you eat butter six months or a year ago and how much per day?
& # 39; Nobody remembers that kind of thing, so you end up with conclusions such as: people who ate an average of 10 grams of butter a day were 20 percent more likely to have heart disease.
& # 39; But that doesn't tell me what effect butter is likely to have on my risk of heart disease. & # 39;
The idea now is that we all need personal nutritional advice – once you know how your own body reacts to different types of food, you can make changes to avoid some and benefit from others.
This work is & # 39; fascinating & # 39 ;, says professor Eran Segal, a biologist at the Weizmann Institute of Science in Rehovot, Israel, and a global specialist in the field of personalized nutrition. He carried out a 900-person study four years ago, which found major differences in blood glucose levels after people ate the same food, but this did not include twins.
He adds: & # 39; The data from twins give a new twist to this research by emphasizing the role of the non-genetic factors that the study has identified.
& # 39; It confirms the need for a personal diet that can have a profound impact on people suffering from diabetes, obesity, and other metabolic diseases. & # 39;
Professor Spector has already made changes to his own eating habits due to the regular use of a 24-hour glucose monitor.
& # 39; If I were to eat a sandwich, I would usually choose brown bread with tuna and mayonnaise because it seemed fairly healthy, & # 39; he says. & # 39; But I discovered it was much worse for my blood glucose than spaghetti Bolognese or a curry with rice.
& # 39; A healthy blood sugar level is around five, and with an orange juice with my sandwich I pushed into the diabetic range at 11. A banana was slightly better, while an apple with the same sugar content had no effect. & # 39;
Since replacing sandwiches with mixed nuts and fruit for lunch, and trying & # 39; eat-anything & # 39 ;, vegetable evening meals, Professor Spector has lost 10 kg in two years.
In theory, the easiest way to follow your body's reactions to food is with one of the glucose monitors used by people with diabetes (see box on the left). & # 39; But you really need a doctor to evaluate the findings & # 39 ;, says Professor Spector.
Another important measure is how much a food affects the fat content in the blood.
ARE YOU A SLOW FAT DIVIDER?
Normally the fat content slowly increases about six to eight hours after a meal (slower than glucose, which takes a few hours) and then begins to decrease.
If your fats take too long to remove them, it can lead to problems such as inflammation and weight gain. It can also interfere with a routine clearing process that takes place in the intestines.
& # 39; When fat remains in the blood, a special type of microbe that acts as the cleanup staff of the gut cannot do their job & # 39 ;, says Professor Spector. & # 39; They only work when no food arrives, so having longer breaks between food is good
for the gut microbes. A fat meal late at night, if your fat clearance is slow, can be a bad combination.
& # 39; The difference between slow and fast clearing may be why some do better on a low-fat diet and others do better on low carbohydrates. & # 39;
That's why snacking can be bad news if you put a lot of fat in your diet, says Dr. Berry. & # 39; Your body is in a constant state of metabolic flux, so that it never gets rest when processing food. & # 39;
As for Kinga and Kata, they think about how they can best respond to information about how their bodies work.
They participated in the trial, partly because & we are identical twins useful for research and we are happy that our data is used to improve people's health & quot ;, says Kinga. But there was another personal motive: & # 39; We were intrigued to know things that could be different between us – we were really surprised by the bowel check.
& # 39; We have a varied diet and get fiber from vegetables. We hoped we would at least have a high average number. & # 39;
Both twins also had a slower pace than normal to remove fat from their bloodstream, which is associated with heart problems and weight gain.
& # 39; We can make some changes – but now we are told not to, & # 39; Kinga adds.
& # 39; We are not in a hurry because we are healthy and our weight has remained the same for about ten years. There is still much to learn. & # 39;
SPOT FOOD PROBLEMS
The researchers are still unraveling the complexity of how food affects our bodies and the role of other factors such as sleep, exercise and even the timing of when you eat.
But if you are interested in getting an idea of the effect that different foods have on you, the easiest way is to see what they do with your blood sugar levels.
In theory you could do this with the type of glucose monitor that people with diabetes use to measure their blood sugar levels – these monitors, which involve a fingertip blood test, cost around £ 20 to £ 30.
A more advanced continuous glucose monitor works through a patch that painlessly attaches to your arm – it costs around £ 150. You should check your response to individual foods, such as a banana, about two hours after eating. However, it is a complicated process and, as Professor Tim Spector, the principal investigator, says that you naturally need a doctor to substantiate the findings.
Another important measure is how much a food affects the fat content in your blood – this should be tested by a clinic.
But the process could be simpler soon, as the team behind the Predict 1 twin study is now developing an app to tell you how your body will respond to almost any food.
With the app, which will be released next year, there will be a test kit for the home, with more user-friendly versions of some of the tests that Predict 1 performs. Your personal profile will be compiled from this.
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