Prof. Dr. Andreas Michalsen from the Charité explains what the daily values, which are mentioned again and again, are all about.
Five meals a day, three large and two small, which contain at least five portions of fruit and vegetables and with which we consume a maximum of 2000 kilocalories, drink two liters, walk 10,000 steps, brush our teeth twice for two minutes and sleep for eight hours – that’s how we live healthy, they say. But where do these values actually come from? And what’s wrong with them?
“In terms of evidence, i.e. the scientific evidence, this precision of the numbers does not exist,” explains Prof. Dr. Andreas Michalsen (60), chief physician at the Institute for Social Medicine, Epidemiology and Health Economics at the Charité. “These are only approximations. You can use them as a guide, as an incentive for a healthier lifestyle. But they should also be enjoyed with caution.”
Why?
► Firstly, because people are individual, emphasizes the doctor, and therefore not all numbers can apply to everyone in the same way.
► Secondly, the incentive character can easily turn into the opposite: “It can quickly become demotivating if you repeatedly fail to reach the goal you have set. Then the numbers often have exactly the opposite effect, you stop trying.”
►Thirdly, you have to consider: “Some numbers are simply outdated because science is now up to date.”
10,000 steps a day
This number was invented in Japan in the mid-1960s: At that time, a pocket watch-like device came onto the market, the manpo-kei – which means something like a 10,000-step counter. The number was a marketing consideration: 10,000 is easy to remember and the symbol for 10,000 in the Japanese kanji characters resembles a running human. So far, so unscientific.
So there’s nothing wrong with that number then? A 2019 Harvard University study found that women who walked an average of 4,400 steps a day had a lower mortality rate than women who walked fewer than 3,000 steps. The mortality rate decreased as the number of steps increased, but only up to about 7500 steps. There was no additional positive effect.
“In principle, every movement is good,” says Michalsen. “But it’s more of a curve than a fixed value: if someone has only taken 1000 steps before and then takes 3000, then that’s good! And if he makes 5000, it’s even better! You can’t say in principle that it’s particularly good if you take 10,000 steps. And you don’t get sick if you don’t do 10,000 steps.”
2000 calories a day
This figure is based on a US Food and Drug Administration survey of eating habits in the 1990s. In it, women stated that they consumed between 1,600 and 2,200 calories per day and men between 2,000 and 3,000. The authority set 2,350 as the average value and rounded off the number to simplify the statement and to counteract excessive calorie intake.
Regardless of how the number came about, Michalsen doesn’t think counting calories makes sense.
“Basically, there are big differences in the energy intake, depending on how much basic energy a person consumes. It depends on gender, height, weight, activity level and other factors. There are thumb values, but they are completely useless,” he emphasizes.
In addition: “No study has been able to prove that people lose weight in the long term by counting calories. This is more likely to be achieved with the right foods, mindful eating and exercise.”
Fruit and vegetables 5 times a day
The “5 a day rule” is based on the WHO recommended minimum daily intake of 400 grams of fruit and vegetables. It is based on “epidemiological evidence of an increased risk of cancer with lower intakes of certain fruits and vegetables”.
A 2017 study at Imperial College London also found that people who eat five servings of fruit or vegetables a day have a 14 percent lower risk of coronary heart disease than those who only eat half.
Prof. Michalsen emphasizes that you don’t have to make absolute judgments here either, but rather observe the development: “Anyone who has previously eaten no or very little fruit and vegetables is doing something good for their body with just two or three portions”, he explains. “And if you eat well in general, you don’t have to worry if you have a day or two without vegetables.”
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5 meals: 3 large, 2 small
This is exactly what the German Society for Nutrition recommends on its website. According to Prof. Michalsen, however, this information is outdated and even wrong!
“At some point doctors realized that if diabetes patients always eat something, then the blood values are very regular because insulin is constantly being released,” he says.
“Today we know that snacking tends to promote the development of fatty liver, diabetes and inflammation. The body would rather have some rest from digestion.” The same applies to the body as to the mobile phone: first let the battery run down completely before you recharge it!
+ Drink 2 liters of water a day
The number goes back to a recommendation by the Food and Nutrition Board of the National Research Council in the USA in 1945: one should drink one milliliter for every calorie consumed. At 2000 calories that would be 2 liters a day. Many took that literally, but according to today’s experts, it meant all liquids, including those in food.
“We don’t necessarily need 2 liters a day,” confirms Prof. Michalsen. “Of course we should drink enough liquids, but we feel thirsty for that. After two sauna sessions or sports that make us sweat a lot, we quickly drink a liter on our own. The body sends signals – we just have to learn to pay attention to them.”
In addition, the fluid requirement also depends on the temperatures: “On a hot summer’s day it can be 3 liters that you need, on a cold winter’s day perhaps only 1.5 liters.”
8 hours sleep per night
Numerous studies have shown that insufficient sleep duration impairs physical and cognitive performance in humans, affects mood, reduces alertness, worsens reaction time. Long-term lack of sleep even increases the risk of dementia.
But does it have to be 8 hours? No! “The amount of sleep required can differ from person to person, depending on the season, the phase of life and many other aspects,” explains the Charité’s chief physician.
“For some, six hours is enough, others need nine hours to really feel good. This is mainly genetic, but also depends on whether you z. B. is stressed or on vacation.”
Brush your teeth for 2 minutes twice a day
We learn from the very first milk tooth that we have to brush our teeth conscientiously in order to avoid tooth decay and gum disease. But does it have to be 2 minutes twice a day? A study at the University of Göttingen came to the conclusion in 2005 that brushing once a day could be enough for good oral health.
However, the dentists also said that most people are not very thorough, so brushing twice a day would be better. In 2012, the Academic Center for Dentistry Amsterdam examined the duration of tooth brushing: With a brushing time of two minutes, around 41 percent of the dental plaque disappeared, while with one minute only 27 percent.
“People who are prone to tooth decay or who eat a lot of sugar between meals may need to brush more than others.”