If you’ve been scanning the diet and weight loss news the past few years, you’ve probably heard about intermittent fasting. Intermittent fasting refers to various patterns of time-dependent eating. Examples include rotating between eating and fasting (or low calorie) days to time-restricted eating within the same day.
What is time-restricted eating?
Time-restricted eating is a type of intermittent fasting. It’s different from other diet strategies as it focuses on when you eat, not on what you eat. It limits your eating to a set window of time each day. The rest of the day is spent in a state of fasting. Now even without time-restricted eating, we usually have a period of 8-10 hours of fasting while we’re sleeping. But for many of us, our first meal is when we wake up and our last meal/snack just before we go to bed. Time-restricted eating targets a much shorter period of eating between 6 and 12 hours, unlike the 14 to 16 hours most of us are used to.
It also differs from earlier nutrition advice recommending snacks throughout the day. Instead, it’s believed our digestive tract, and related metabolism, need periods of rest from breaking down and metabolizing food. And unlike a lot of other popular diet trends, time-restricted eating is more than just weight loss, but also about metabolic health.
This eating pattern has its origin in how our ancestors ate, going through periods of feast and famine as access to food was limited. It’s only been in the past century that food has been plentiful for a large number of people. Therefore, for thousands of years the human body has got used times of not eating. In essence, we’ve evolved being exposed to some sort of eating/fasting pattern.
But just because our ancestors ate a certain way, doesn’t mean it’s the best option. Life expectancy has increased remarkably over the past 50 years and improvements to nutrition are one reason why. However, there may be more to intermittent fasting than just being the latest diet fad.
Health Benefits of Time-Restricted Eating
As with many diets, people turn to time-restricted eating for weight loss. And why not? It’s often touted as being a diet plan in which you can eat what you want. Whether effective at weight loss is not entirely clear. Small studies in which meals were limited to ten hours or less have demonstrated weight loss in people with the metabolic syndrome and those with obesity.
However, the largest and most robust study found no real effect on weight. In this 12-week study in people who were overweight, eating over eight hours resulted in only a slightly greater amount of weight loss compared to people eating over a 16 hour window. People were allowed to eat what they wished and there was no attempt to ensure both groups ate the same thing.
While these findings dispel the notion one can eat what they want, it may not mean time-restricted eating is no good. When diets were managed, time-restricted eating led to more fat mass compared to a control diet group. In the end it may mean that what you eat is still important. If your diet is high in highly processed and sugary foods, your chances for disease are high regardless of when you eat.
But the benefits of time-restricted eating are not just limited to weight loss. In men at risk for type 2 diabetes, five weeks of time-restricted eating improved blood sugar metabolism and blood pressure compared to when the same men underwent a control condition eating over a 12 hour period. This occurred despite no apparent changes in weight.
How does it work?
Time-restricted eating may work in two ways. The first, it may actually lead to a reduction in hunger and improve the use of fat as an energy source. The second, it aligns periods of eating with the body’s natural internal clock (circadian rhythm).
Your circadian rhythm regulates a number of processes, which affect how we use or store food we eat. One way is through the hormone melatonin. Melatonin is released by the brain and is best known as the sleep hormone. One of its actions is on the pancreas to get it to stop making insulin. Insulin is responsible for keeping your blood sugar from going too high. When you eat a meal, insulin is released to clear the sugar away into the muscles, liver and other organs for energy use.
At nighttime when melatonin is released, it stops the production of insulin allowing sugar to stay in your blood longer. This may seem counter intuitive as we know that excess sugar can lead to diabetes and heart disease. However, when you’re asleep, you actually need sugar in your blood as you’re not eating for an 8 to 10 hour period. Your body uses that energy to keep it running. Thus, melatonin reduces insulin to ensure you have sugar readily available during the long period of sleep.
When you eat a meal close to bedtime, blood sugar levels remain high as insulin is not available. Doing this regularly may increase your chances for diabetes and heart disease through increases in blood sugar and cholesterol. Eating before bedtime can also lead to more disturbing dreams, possibly due to effects of the meal sitting in your stomach being digested. Time-restricted eating encourages eating earlier in the day to prevent these metabolic problems.
Is time-restricted eating right for you?
Plenty of people swear by time-restricted eating to help them in maintaining their weight and improving their health. And it’s a diet pattern that can be combined with other plans as well. At present, the evidence supporting time-restricted eating is rather weak. But there’s biological backing to indicate time-restricted eating may make sense. It’s quite likely the ideal study hasn’t been conducted. And we need to remember, studying diets is hard, so it may take time for that study to be done.
A few years ago, I started my own style of time-restricted eating in which I stopped eating after 7 pm. I was snacking on chocolate before bedtime and wanted to break that habit. I also began taking evening walks. While I wasn’t doing if to lose weight, after four months, I was eight pounds lighter. I’m not perfect at sticking with it everyday but most days I do.
Time-restricted eating may not be for everyone. Some people end up eating more for fear they’ll be hungry later on. You may also be concerned how it will affect your exercise. The studies to date don’t address that directly but suggest it shouldn’t be a problem. And if you’re doing shift work or working late at night, time-restricted eating might not fit your schedule. In the end, the most effective diet plan for you is one that fits into your life.
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