Prof. Dr. F. Perry Wilson is an associate professor of medicine and public health and director of the Clinical and Translational Research Accelerator at Yale and a regular commentator on Medscape.com . In his current blog (you can find the original video in English here ) he presents a study on intermittent fasting (time restricted eating) in metabolic syndrome and discusses whether this is a “ Magic Bullet” could act. The transcript has been edited for readability.
Welcome to Impact Factor your weekly dose of commentary on new medical studies. I am Dr. F. Perry Wilson from Yale School of Medicine.
One in 3 American adults – about 100 million people in the US – has metabolic syndrome. I’ll show you the official criteria here (see graphic), but essentially it’s a syndrome of insulin resistance and visceral obesity that predisposes us to a variety of chronic diseases such as diabetes, heart disease and even dementia.
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Metabolic syndrome is essentially a lifestyle disease. There is a direct link between our dietary habits and the wide availability of high-carbohydrate, highly processed foods and the rise of the syndrome in the population.
A saying that I learned from one of my epidemiology lecturers comes to mind: “Lifestyle diseases require a change in lifestyle.” But you know what? I’m not so sure about that anymore.
I’ve been a doctor long enough to see several nutritional recommendations come and go with varying degrees of effectiveness.
I grew up in the low-fat diet era, which was probably the most damaging time for our national health – namely, when food manufacturers began replacing fats with carbohydrates. This caused much of the problems we face today.
But I’ve also experienced the Atkins diet and the low-carb diet – all in all, a healthier approach. And I’ve seen different variations of it: the Paleo diet (essentially a low-carb, high-protein diet based on as few processed foods as possible) and the Mediterranean diet, which tried to replace a certain amount of fats with healthier fats.
And of course there is the time-restricted diet.
Time-restricted eating, a variation of intermittent fasting, has the advantage of being very simple: no cookbooks, no recipes. Eat whatever you want – but limit it to certain hours of the day, ideally a window of less than 10 hours, for example from 8 a.m. to 6 p.m.
When it comes to weight loss, all diets that reduce calorie intake work. I know a lot of people will be upset about this, but thermodynamics is not just a good idea, it’s a law.
But weight loss isn’t the only reason we should eat healthier. What we eat can affect our health in many ways: certain foods lead to more atherosclerosis, more inflammation, increased stress on the kidneys and liver, and can affect our glucose homeostasis.
So I was really interested when I read this article “Time-Restricted Eating in Adults With Metabolic Syndrome” (“Time-Restricted Eating in Adults with Metabolic Syndrome”), which was recently published in the Annals of Internal Medicine has appeared. Here the effect of time-restricted eating on the metabolic syndrome itself was examined. Could this lifestyle intervention cure this lifestyle disorder?
In the study, 108 people, all of whom had metabolic syndrome but not diabetes, were randomized into a usual care group – essentially nutritional education – and a time-restricted diet group. In this group, participants were instructed to shorten their eating window by at least 4 hours to achieve an 8- to 10-hour eating window. The groups were followed for 3 months.
Before we get to the results, I would like to remind you that the success of a lifestyle intervention study depends heavily on how well the participants adhere to the lifestyle intervention. A time-restricted diet is not as simple as taking a pill once a day.
The researchers had participants log the foods they consumed using a smartphone app to check whether they were sticking to this restricted eating window.
By and large, the participants did the same. At the start of the study, both groups had an eating window of around 14 hours a day – for example, from 7 a.m. to 9 p.m. The intervention group reduced this time window to just under 10 hours, with 10% of days falling outside the target window.
This is how a change in lifestyle was achieved. The primary outcome was change in hemoglobin A1c at 3 months. The HbA1c value indicates serum glucose levels over time and is therefore a good indicator of the success of the intervention in relation to insulin resistance. But the effect was, frankly, disappointing.
Technically, the time-restricted diet group had a greater change in HbA1c levels than the control group – by 0.1 percentage points. On average, their HbA1c increased from a baseline of 5.87 to a 3-month HBA1c of 5.75.
Other markers of metabolic syndrome were also unremarkable: no difference in fasting blood sugar, mean blood sugar, or fasting insulin.
However, there were some changes in weight: the control group that received the nutritional education lost 1.5% of their body weight over the 3 months. The time-restricted diet group lost 3.3% – about 3kg, which is reasonable.
This weight loss resulted in statistically significant, although small, improvements in BMI, body fat percentage, and LDL cholesterol.
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What’s interesting is that despite the greater weight loss in the intermittent fasting group, there was no difference in muscle mass loss – which is encouraging.
In conclusion, a time-restricted diet can help people lose some weight. This is essentially because people consume fewer calories when they follow a time-restricted diet, as you can see here.
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Ultimately, however, this study was looking at whether this relatively simple lifestyle intervention would lead to improvements in metabolic syndrome – and the data for this isn’t very compelling.
This graph shows how many of these 5 metabolic syndrome criteria the people in this study had from start to finish. You can see that over the 3 months, 7 people in the time-restricted group dropped from 3 criteria to 2 or 1. So you were “cured,” if you will, of metabolic syndrome. But 9 people in the control group were also cured according to this definition. As a reminder, participants had to meet at least 3 metabolic syndrome criteria to be eligible for the study.
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So I’m wondering if time-restricted food intake really has magical effects on metabolism. If it only results in weight loss by forcing people to eat fewer calories, then we must acknowledge that we probably have better methods of achieving the same goal.
10 years ago, I would have said that lifestyle changes were the only way to end the epidemic of metabolic syndrome in this country. Today we live in a world with GLP-1 weight loss drugs. It’s just a different world. Yes, they are expensive. Yes, they have side effects. However, we must weigh them in comparison. And so far, lifestyle changes alone are no comparison.
This article was originally published on Medscape.com . As part of the translation process, our editorial team may also use text editing software including AI.
