No diet or exercise, get a slim body in 3 months without spending a dime!” This is not a false weight loss advertisement, but the results of a time-limited diet study recently published in the journal Cell-Metabolism. The journal is authoritative and the results are tantalizing, but immediately using this method to lose weight, you’re in too much of a hurry.
Time only, all-you-can-eat
This new trick called a time-restricted diet means that you are only allowed to eat and drink for a certain number of hours each day, and fast at other times (water without energy is allowed). There are no restrictions on what and how much you can eat during the time you are allowed to eat.
For example, a 10-hour eating restriction: start breakfast at 9:00 and eat whatever you want in between, but the last meal has to be over by 19:00, and then you can’t eat anything until breakfast the next day.
Another term that has become popular in recent years is “intermittent fasting”, and time-limited diets are a type of intermittent fasting. Since studies have shown that intermittent fasting is effective in short-term weight loss and also improves blood lipids and blood glucose, people are looking forward to time-restricted diets.
Lower body weight and waist circumference, and improvement of the “three highs”.
The study was conducted in California, USA, with 19 participants (13 of whom were male) who had metabolic syndrome and normally ate for at least 14 hours per day .
Participation consisted of downloading a smartphone app called “myCircadianClock”, following the prompts to limit eating to 10 hours per day, and recording what they ate. Compared with the complicated weighing of food when limiting total energy, the time-limited diet is very simple to operate.
Not only is it easy to follow, but it’s also easier to stick to than diet and exercise. Most of the participants in the study were able to follow the diet for 3 months without serious discomfort, and after 3 months, not only did the participants lose an average of 3.3 kilograms, they also lost body fat percentage and waist circumference (waist circumference decreased by an average of 4.5 centimeters). This rate of weight loss was comparable to the effect of abstinence plus exercise. At the same time, participants had lower blood pressure and blood lipids, and a slight improvement in blood glucose.
The results were so good that most people spontaneously continued the time-restricted diet after the study ended. More than a year later, a quarter of the participants were still on the time-restricted diet every day.
One study doesn’t count.
Effective though it may be, the conclusions of a single study alone are not convincing enough. Time-restricted diets have also recently been supported by the results of other studies: a 3-month time-restricted diet can significantly reduce body weight and waist circumference in overweight and obese people without increasing the amount of exercise .
Even if short-term weight loss is effective, it still has to be possible to adhere to it in the long term to be meaningful. Regarding the ease of adherence to a time-restricted diet, 40% of participants found it easy to adhere to and only 10% found it difficult . Most obese people can adhere to time-restricted diets as low as 8 hours, and their sleep and poor eating behaviors improved rather than worsened .
Long-term dieting can easily lead to malnutrition, but when people went on time-restricted diets, they did not reduce the amount of healthy foods such as vegetables and fruits, they just reduced the amount of snacks. Not only did they eat healthier, but some people’s blood pressure, blood lipids and blood glucose levels also improved during the time-restricted diet .
Some people are concerned about losing muscle with prolonged fasting, and some studies have shown that short-term time-restricted diets in men with regular amateur strength training do not lead to a decrease in muscle size or strength .
Are time-restricted diets so effective just because you eat less or is there something else going on?
Why can you eat whatever you want and still lose weight?
In terms of total dietary energy, although these studies did not restrict food composition or quantity, because the window in which you can eat is shortened, you can’t eat as much until you are full. Changing from an unrestricted diet to a time-restricted diet can reduce energy intake by hundreds of kilocalories per person per day on average. In addition, most people usually like to eat fattening snacks in the evening, and time restriction reduces the opportunity to eat these snacks, which also facilitates weight loss.
In addition to energy and composition, eating time also affects weight. Many people “three meals small bird stomach, snacks do not stop mouth”, only in the early morning before going to bed to six or seven o’clock in the morning to let the stomach and intestines a short break . Such a long and irregular eating habit can affect the human biological clock (circadian rhythm).
The human biological clock in the brain is not only regulated by light, but diet is also an important influence [9, 10]. Long-term mismatch between eating and fasting times can interfere with the biological clock and affect the balance of endocrine, autonomic nervous system and nutrient metabolism, increasing the risk of obesity and “three highs” .
A time-restricted diet may lead to more regular eating and sleeping times, and no more late-night eating. A better adjusted biological clock is conducive to weight loss, and some people also have better sleep quality and better overall health .
Don’t rush to lose weight on a time-restricted diet just yet
Since time-limited diets are so simple and effective, wouldn’t it be better to download a mobile app right away and sit back and wait to get thinner? Don’t worry.
1、You don’t always lose weight.
First, while most time-limited diet studies have promising results, the small total number of relevant studies and the small number of participants in each study make the conclusions not necessarily reliable.
Second, some of the studies did not have a control group, and participants may have been embarrassed to eat so much unhealthy food because they knew they were participating in a diet-related study (the cueing effect caused by the unlimited, app-only downloads and logging of diets may have been weight loss as well).
On the participant side, most studies with substantial weight loss results have targeted overweight and obese populations. One study showed that shortening the eating time did not reduce weight when enrolling normal-sized people who had recently stabilized their weight [18].
In addition to body size, most of the participants originally ate for a long time and did not control their dietary energy. So if you are in the normal range for your body type, don’t eat for a long time each day in the first place, or are already on a controlled diet, a time-restricted diet may not be effective for weight loss either.
2、Reasons why it’s hard to hold on
Although the adverse effects of time-restricted diets are relatively few and mild, there have been cases of people experiencing dizziness, headache, nausea, vomiting, diarrhea and constipation, and as a result, they are unable to continue with them. Moreover, due to the long duration of fasting, if you have any endocrine system abnormality (abnormal blood sugar level, etc.), you should consult your doctor in advance to see if it is feasible.
Finally, most of the enjoyable get-togethers related to eating and drinking are scheduled in the evening, and as soon as the first meal is a little earlier, you cannot participate. This makes it difficult for party-lovers to stick to a restricted diet for long periods of time.
What can we do now?
Restricted diets don’t necessarily make you thinner, and weight loss can start by cutting down on what you eat at night. This reduces the total energy of your diet throughout the day on the one hand and results in fewer unhealthy snacks. On the other hand, it is more in line with the body’s biological clock, which leads to better weight loss and better health.