Nutritional research publications can be maddening. Their sheer volume is overwhelming, but once the poorly done studies are filtered out, once you eliminate the ones that may have some statistical but no clinical significance, get rid of the ones that make grandiose claims about health effects based on food questionnaires administered on a single occasion, purge the ones that over-interpret results based on too few subjects, exclude those that imply long term effects based on short term trials, and disregard studies that unrealistically extrapolate animal data to people, you don’t have much left to chew on. But let’s nibble away at the studies that explore the current hot topic in “wellness,” which is “time-restricted eating.” The proposition is that when it comes to health status, it is not only what we eat that is important, but also when we eat.
While there certainly is controversy about details, there is a general consensus about the “what.” A diet should be based mostly on vegetables, fruits and whole grains, with minimal processed foods, especially ones high in sugar and salt. Fish is preferred over other flesh foods, and extra-virgin olive oil over refined seed oils. Saturated fats, such as in butter and in red meat should be limited, as well as foods charred by high heat. Alcohol no more often than a couple of times a week, and soft drinks as close to never as possible. With that out of the way, let’s get down to the “when.”
It was back in 1935 that Cornell University nutritionist Dr. Clive McCay discovered that mice fed a diet that reduced calorie intake by 30% were physically more active and far less prone to diseases of advanced age than their free-grazing laboratory mates. Furthermore, they lived about 40% longer! At the time, the interpretation was that the benefits were due to a reduced production of tissue-damaging “reactive oxygen species (ROS)” that are by-products of the reaction between glucose and oxygen, the reaction that produces the energy needed to fuel the life processes in cells. Chemically speaking, ROS are “free radicals,” electron-deficient species that are ready to steal electrons from any molecule they may encounter. Since electrons are the “glue” that bind atoms together in molecules, their loss results in bond breakage. Should the molecules affected be proteins or nucleic acids, the consequence can be disease or accelerated aging. But if there is less food to metabolize, goes the argument, fewer free radicals are produced with the result being enhanced longevity.
Since McCay’s original observation, numerous studies using fruit flies, mice, dogs, and monkeys have demonstrated that caloric restriction increases longevity. However, reduced free radical formation may not be the only factor involved. Not recognized in the early rodent experiments was the fact that the animals consumed their restricted food allotment within a few hours of it being provided, meaning that they had long periods of fasting.
In a normal state, cells “burn” glucose, provided by the diet, to produce the energy needed to sustain life. In a fasting state, with no glucose being provided, a back-up system is engaged. Cells, instead of “burning” glucose, switch to metabolizing stored fats. This involves the breakdown of fats to yield acetone, acetoacetate, and beta-hydroxybutyrate, the so-called “ketone bodies” that serve as an alternate fuel for energy production. But “ketosis,” as this fat-burning process is called, is also a signal to the body that there is no food coming in, a crisis situation. The “metabolic switch” to burning ketones instead of glucose then triggers a number of cellular responses aimed at survival. Cells begin to crank out various molecules that repair DNA, reduce inflammation, regulate glucose sensitivity and break down damaged cells (autophagy). All these processes can benefit health.
This brings up the question of whether the benefits of a calorie-restricted diet seen in animals may be a function not only of the reduced calorie content, but also of the time frame during which no food is consumed. Is there an optimal way, researchers wondered, to incorporate fasting into a dietary regimen? What if instead of just cutting down on calories, attention were paid to when the meals that make up that restricted calorie diet are eaten? Thus was born the concept of “time-restricted eating,” or its alternative designation, “intermittent fasting.”
Several regimens have been proposed. Eating a regular diet on 5 days and cutting calories down to 500-700 on two days a week (5:2 fast), doing the same on alternate days of the week (4:3 fast), or fasting for 14-16 hours a day (daily time-restricted eating) have all been tried. In the latter case, no restrictions are placed on calories during the 8-10 hours when food is consumed, but experiments have shown that this automatically results in a reduction of calories because night-time snacking is eliminated. While most of the trials involving these regimens have resulted in weight loss, the benefits such as improvement in glucose regulation, blood pressure, inflammation, and loss of abdominal fat, go beyond what would be expected for weight reduction. For example, in one study, women were assigned either to a 5:2 intermittent-fasting regimen, or a daily 25% reduced calorie diet. Over 6 months, both groups lost the same amount of weight, but the 5:2 group had improved insulin sensitivity and a larger reduction in waist circumference.
Other studies involving intermittent fasting have shown better running endurance, improvements in the HDL/LDL cholesterol ratio, reduction in free radical activity and reduced markers of systemic inflammation. Some preliminary studies have also shown suppressed tumour growth in a number of cancers. In animal models, alternate day fasting can delay the onset and progression of neurological diseases such as Alzheimer’s, Parkinson’s, and multiple sclerosis. There are even suggestions that intermittent fasting can improve memory and cognitive performance.
The evidence of benefits continues to accumulate. In a widely quoted study, one group of mice was given access to food only during a 9-hour period, while those in a control group were able to eat whenever they liked. The two groups actually ended up eating roughly the same amount of food, so at least in this case, whatever results were obtained could not be ascribed to a difference in caloric intake. After 7 weeks, tissue samples were taken from multiple organs and examined for any changes in gene expression. Genes code for the production of proteins, so basically the researchers measured whether the production of various proteins increased or decreased. Genes that code for proteins responsible for inflammation were found to be less active, while genes that produce proteins that repair damage to DNA and ones that inhibit cancer cell survival geared up. But, of course, mice are not men or women.
So, what about men or women? One interesting study examined changes in a number of proteins produced as a result of eating only during a 10-hour period and fasting for 14 hours. The subjects, 8 men and 6 women, were all observers of the Muslim religious month of Ramadan during which no food or drink is consumed between dawn and sunset. They were specifically selected because each one met at least three criteria of “metabolic syndrome,” defined as central obesity, insulin resistance, high blood pressure, high levels of triglycerides, and high cholesterol. These parameters are easily monitored and can provide information about the health effects of fasting in addition to changes in gene expression.
All of the markers of metabolic syndrome shifted in the right direction during the month of the 14-hour fast, as did proteins involved in destroying cancer cells, repairing DNA, and improving immune function. All very interesting, but the experimental group was small and the study period of a month was short. Also, the subjects all had metabolic syndrome, and calorie intake was not considered. Basically, not much can be inferred as far as the general population goes.
That though is not the case for a study that compared the effects of eating an early or late dinner on glucose levels, insulin production, triglyceride levels and fatty acid oxidation which is a measure of ketosis. Subjects ate their dinner either at 6 or 10 PM, and then had their blood chemistry monitored every hour through an intravenous line. The late dinner resulted in greater glucose intolerance and reduced fatty acid oxidation, both of which can promote obesity. Why should this happen? During sleep, metabolism normally winds down since the body needs less energy. Therefore, ingested glucose and fats are not burned for energy, but rather end up being stored as fat. If dinner is eaten earlier, metabolism remains active until sleep time and less fat ends up being stored. This study would seem to corroborate the benefits of the daily time-restricted fast since if no food is eaten after late afternoon, the reduced metabolism associated with sleep is less of an issue because most of the food will have been metabolized in the 5 or 6 hours between the last meal and sleep.
Now, just as I was ready to wrap things up with a final praise of intermittent fasting schemes, I learned of two recently published papers in respected journals. One found that in adults over the age of 40, a time interval of fewer than 4.5 hours between meals, which essentially means time-restricted eating, was associated with earlier death! Yikes! The second study asked participants to use an app to record the timing of their meals and then went on to relate this to their body weight as documented in their medical records over a ten-year period. Weight changes were not associated with the time between the first and last meals, which would seem to argue against trying to lose weight by time-restricted eating.
Where does all this leave us? As is the case with almost every aspect of nutrition there is controversy, and studies can be found to back up each side. Separating the wheat from the chaff is challenging and requires an extensive review of studies to try to get a handle on the preponderance of evidence. At this point, that evidence indicates caloric restriction to be a factor in reducing markers of disease and longevity, but to make recommendations, especially ones that are difficult to institute, we need more than markers. We need long-term human trials, with a significant number of subjects that compare regular diets, reduced calorie diets, and intermittent fasting with end points of disease or death. Such lengthy trials are difficult if not impossible to finance, organize and monitor. In their absence, we are reduced to making educated guesses.
Since none of the calorie-restricted regimens has shown any risk, there seems to be no harm in giving one or another a shot, whether it be for weight loss or just enhanced health and perhaps a longer life. But I suspect most people would not be able to endure calorie restriction over the long term. There is just too much pleasure to be had from eating. However, having an early dinner and then fasting until bedtime may be a challenge that can be met and may be worth a try. At least until the next study comes out telling us that life expectancy in Spain, where dinners are traditionally eaten late at night, is longer than in North America.
Obviously, the field of nutritional research is very fertile and there are many plants to harvest, but we do have to watch out for the weeds.
Is time-restricted eating worth it? ›
That's according to research published today in JAMA Internal Medicine that found that early time-restricted eating for a period of 8 hours between 7 a.m. and 3 p.m. led to more effective weight loss, blood pressure control, and mood improvement in adults with obesity when compared with a group who ate in an eating ...Is time-restricted eating good for weight loss? ›
In a secondary analysis of completers, early time-restricted eating was more effective for losing weight and body fat. Meaning Early time-restricted eating was more effective for weight loss than eating over a window of 12 or more hours; larger studies are needed on fat loss.Is time-restricted eating no better than counting calories? ›
Time-restricted eating has no significant benefits compared with simple calorie restriction in battling obesity, a new study said. To track compliance, study participants were asked to keep food diaries and photograph all food they ate.How long should you do time-restricted eating? ›
Unfortunately, there isn't enough research on time-restricted eating to know which duration of eating window is best. However, most people use windows of 6–10 hours each day.Why you should not restrict your eating? ›
Restriction can lead to bingeing. Dieting and food restriction have been shown to increase the risk of binge eating. When you feel deprived, you're more likely to overeat once you stop restricting. This restrict-binge cycle is the opposite of a moderate, balanced, peaceful approach to food and eating.Is there no benefit intermittent fasting? ›
"Time-restricted" eating has become a popular weight-loss tactic, but a new clinical trial finds no benefits in adding it to old-fashioned calorie-cutting.Does eating in an 8 hour window work? ›
A 2018 study indicates that in addition to weight loss, an 8-hour eating window may help reduce blood pressure in adults with obesity. Other studies report that intermittent fasting reduces fasting glucose by 3–6% in those with prediabetes, although it has no effect on healthy individuals.What are the benefits of not eating after 3pm? ›
Blood pressure improved
The study found that people who stopped eating at 3pm lost almost a stone over 14 weeks, while the control group lost only about nine pounds. The researchers found that combining a diet with the time restriction equates to losing around an extra five pounds.
According to some researchers, fasting for 10–16 hours can cause the body to turn its fat stores into energy, which releases ketones into the bloodstream. This should encourage weight loss.Why you shouldn't restrict calories? ›
It Can Cause Fatigue and Nutrient Deficiencies
Regularly eating fewer calories than your body requires can cause fatigue and make it more challenging for you to meet your daily nutrient needs. For instance, calorie-restricted diets may not provide sufficient amounts of iron, folate or vitamin B12.
Is overeating better than Undereating? ›
Research shows that being underweight is MORE harmful to your body than being overweight. If you're not eating enough energy, you're literally starving yourself. If you're severely under eating, your body functions will eventually start to shut down and it will likely lead to serious health complications.Is it better to fast or restrict calories? ›
Conclusions. Among patients with obesity, a regimen of time-restricted eating was not more beneficial with regard to reduction in body weight, body fat, or metabolic risk factors than daily calorie restriction.How long does it take to see results from 18 6 intermittent fasting? ›
After the first week of intermittent fasting, you'll probably notice less bloating and a tighter, slimmer look and feel to your midsection. Some people will enjoy some weight loss by week two, but don't be discouraged if your weight scale hasn't budged. Continue for another 4-6 weeks, and you should see changes.Should you stop eating after 7pm? ›
Experts claim, that restricting your meal intake in the window of 6 a.m. to 7 p.m. can reduce the overall calorie intake drastically. This could be because you are most likely to consume fewer calories as the time you have spent in eating has come down.
Follow a five-day schedule.
Time-restricted eating has benefits way beyond weight management, but if you find it difficult to stick to the schedule 24/7, try to give yourself grace on the weekends. "Five days a week is sufficient for people to see benefits in the long term," assures Peterson.
Often times, diet culture encourages us to cut out entire food groups (like carbohydrates) to lose weight and makes us believe that some foods are “good and bad,” “real and fake,” and “clean and dirty.” When we associate carbohydrates with gaining weight and losing weight, it only creates food fear, guilt, and even ...Should we watch while eating? ›
“Moreover, screen time while eating increases children's risk of obesity, as they tend to eat more while they are watching TV. This is because they would be less aware of how much they are eating.How can I eat healthy without restricting? ›
- Choose mindfully, even with healthier foods. Ingredients and nutrient content can vary a lot.
- Read labels. ...
- Watch your calories. ...
- Eat reasonable portions. ...
- Cook and eat at home. ...
- Look for the Heart-Check mark to easily identify foods that can be part of an overall healthy eating pattern.
Intermittent fasting can have unpleasant side effects. They could include hunger, fatigue, insomnia, irritability, decreased concentration, nausea, constipation and headaches. Most side effects go away within a month.Who should not do intermittent fasting? ›
Some people should steer clear of trying intermittent fasting: Children and teens under age 18. Women who are pregnant or breastfeeding. People with type 1 diabetes who take insulin.
Can you lose weight with 16 8 intermittent fasting? ›
With 16/8 intermittent fasting, you restrict your food intake to an 8-hour window and fast for the remaining 16 hours. This practice may support weight loss, improve blood sugar, and increase longevity.Why am I gaining weight with intermittent fasting? ›
You're Not Eating Enough Protein
If you don't, you'll end up feeling hungry, which can result in you eating more. Langevin said, "The basic idea is that IF is a tool, but if you're not paying attention to calorie intake, or a balanced intake during your eating window, that can backfire," and result in weight gain.
- Improved fat burning.
- Improved weight loss.
- Reduced risk of cancer.
- Optimized hormone levels.
- Improved cholesterol levels.
- Improved body composition.
- Better blood sugar regulation.
- Reduced risk of heart diseases.
Not only has it been proven to be beneficial for weight loss and management, but you're also likely to sleep better since your body has had time to digest the food you ate hours prior. Research has found that people who eat earlier benefit from better heart health than those who don't chow down until later at night.Is it good to stop eating at 4pm? ›
Consuming all meals before 3pm and not eating in the evening boosts all round health and helps people lose weight, research shows. A leading international expert reviewed 250 studies and concluded that fasting for at least a regular 14 hours daily boosts overall health.What are the benefits of not eating after 4pm? ›
According to them a cut in daily calories by a fifth can also ward off lifestyle diseases such as cancer and diabetes. Their study, published in the journal Nature Communications, follows research showing that fasting in middle age, or going without food after dark, can help people to live longer, healthier lives.Does sleep count as fasting? ›
Does sleeping count as fasting? A. Yes, while following intermittent fasting, sleeping is considered a fasting period. Therefore, one does not consume food or drinks during this state.What happens after 1 week of intermittent fasting? ›
In the first week, you may also find it difficult to get proper sleep at night. At night you may feel famished or thirsty. You may even wake up frequently just to drink water and may find it difficult to fall asleep again. It happens due to calorie restriction and changes in lifestyle patterns.Is it better to fast for 12 or 16 hours? ›
What is 'fasting' and how does it work? A good rule of thumb for those wanting to fast to improve their metabolic and overall health is to leave at least 12 hours between meals – ideally more – on a regular basis, according to Dr Adam Collins, Principal Teaching Fellow in Nutrition at the University of Surrey.Is 1200 calories too restrictive? ›
Calorie needs are highly individualized and depend on many factors, including body size, age, and activity levels. A 1,200-calorie diet is inappropriate for most adults, including smaller women.
Is 1500 calories too restrictive? ›
Some people may choose to restrict their daily intake to 1,500 calories. While factors such as age, gender, and activity level can cause caloric needs to vary, a 1,500-calorie intake is typically less than the average person requires. As a result, this diet may help some people lose weight.Why am I gaining weight when I'm eating less and working out? ›
You've gained muscle.
And here's an often overlooked fact: Muscle tissue is more dense than fat tissue. So as you gain more muscle and lose fat, you change your overall body composition, which can result in a higher weight, but a smaller figure and better health.
Once you are an adult, your stomach pretty much remains the same size -- unless you have surgery to intentionally make it smaller. Eating less won't shrink your stomach, says Moyad, but it can help to reset your "appetite thermostat" so you won't feel as hungry, and it may be easier to stick with your eating plan.What happens if you train hard but don't eat enough? ›
"If you do a moderate-high intensity workout without properly fueling, your blood sugar can drop very low, making you feel dizzy or faint," Matheny explains. You're also likely to feel straight-up tired or lethargic if you're not giving your body energy, yet are demanding a lot from it during a tough workout.What are the negative effects of caloric restriction? ›
Reduced energy intake is also associated with an increased likelihood of failing to reach dating nutritional needs. In severe caloric restriction, diets may not be sufficient to provide adequate amounts of folate, iron, or vitamin B12. This can subsequently lead to fatigue and anemia.Is it better to eat faster or slower? ›
Eating too quickly can lead to weight gain and decreased enjoyment of food. However, slowing down can increase fullness and promote weight loss. It also provides other health benefits. If you minimize your screen time, chew more, and focus on high-fiber foods, you'll be well on your way to slower eating.Will I lose weight if I restrict calories? ›
Your weight is a balancing act, but the equation is simple. If you eat more calories than you burn, you gain weight. And if you eat fewer calories and burn more calories through physical activity, you lose weight. In the past, research found about 3,500 calories of energy equaled about 1 pound (0.45 kilogram) of fat.Is 18 6 fasting better than 16 8? ›
When comparing the intermittent fasting 16:8 vs. 18:6, it is clear that for those who are new to such an eating approach, the 16:8 fasting may be better, as it has a bigger eating window. Both these types require that you don't eat anything during your fasting period, and both have similar benefits.Why am I not losing weight after intermittent fasting? ›
You underestimate portions
If you're not losing weight—despite staying within your calorie needs—then it's time to look at serving sizes. It's common to miscalculate how much you're actually eating. This is particularly true with calorie-dense foods such as cheese.
But according to the information above, in terms of insulin level, the fast is only really getting going at 16 hours. Extending it further than this ramps the drop in insulin and the increase in lipolysis. If you can extend your fast into the afternoon, you get more benefits, and a 24-hour fast would do even more.
Can I fast from 7pm to 7am? ›
Having a decent overnight fast may be a great place to start to give your gut bacteria a helping hand. Having a 10-12-hour overnight period, say 7pm-7am where no food is consumed, is a very traditional way of eating.When should you eat your biggest meal? ›
Most people are brought up thinking that dinner should be the biggest meal of the day, meaning they opt for a light breakfast and lunch. However, research has found that a smaller dinner and larger lunch could be the key to helping you shift those weight.What hour of the day should you stop eating? ›
As a guideline, you should stop eating two to three hours before bed. This will give your body enough time to digest your food, lowering your chances of acid reflux and digestive issues keeping you up.Can you lose weight with time-restricted eating? ›
In a secondary analysis of completers, early time-restricted eating was more effective for losing weight and body fat. Meaning Early time-restricted eating was more effective for weight loss than eating over a window of 12 or more hours; larger studies are needed on fat loss.Did scientists find no benefit to time-restricted eating? ›
At the end of the year-long study, researchers found that time-restricted eating had no effect on their weight loss, body fat, or metabolic risk factors such as blood pressure, blood sugar, and cholesterol. Case closed.What are the benefits of not eating for 16 hours? ›
If you don't eat for 10–16 hours, your body will go to its fat stores for energy, and fatty acids called ketones will be released into the bloodstream. This has been shown to protect memory and learning functionality, says Mattson, as well as slow disease processes in the brain.Is it better to eat at set times or when hungry? ›
In general, scheduling what and when you eat will help you maintain a balanced diet and create a more stable energy source, as your metabolism will be engaged at optimal levels all day long. The goal is to eat every 3 to 4 hours in order to keep your blood sugar consistent and for your stomach to optimally digest.Does time-restricted eating build muscle? ›
A long term study has shown that a time-restricted eating protocol helped strength-training participants lose weight and quell inflammation. But they lost muscle as well as fat, primarily because their testosterone levels were depressed.What is the 20 minute rule for eating? ›
It takes approximately 20 minutes from the time you start eating for your brain to send out signals of fullness. Leisurely eating allows ample time to trigger the signal from your brain that you are full. And feeling full translates into eating less.Is it better to fast 12 or 16 hours? ›
A good rule of thumb for those wanting to fast to improve their metabolic and overall health is to leave at least 12 hours between meals – ideally more – on a regular basis, according to Dr Adam Collins, Principal Teaching Fellow in Nutrition at the University of Surrey.
What are the negatives of intermittent fasting? ›
2. Skipping Meals Can Cause Headaches, Dizziness, and Nausea. Long periods of fasting can lower your blood sugar levels and leave you feeling lightheaded, dizzy, with headaches, and/or nausea. If you have a medical condition, talk to your doctor to make sure it's safe to try intermittent fasting.What is the most optimal time to eat? ›
Plan to eat breakfast within an hour of waking. This way, your breakfast doesn't blend into a mid-morning snack or grazing followed closely by lunch. Lunch should be about four to five hours after breakfast. For example, if you ate breakfast at 7 am, eat lunch between 11 am and noon.Can you do 16 8 fasting every day? ›
You can pick a daily approach, which restricts daily eating to one six- to eight-hour period each day. For instance, you may choose to try 16/8 fasting: eating for eight hours and fasting for 16. Williams is a fan of the daily regimen: She says most people find it easy to stick with this pattern over the long term.Is eating 1 time a day healthy? ›
Safety Concerns. For most people, there are no serious dangers involved in eating one meal a day, other than the discomforts of feeling hungry. That said, there are some risks for people with cardiovascular disease or diabetes. Eating one meal a day can increase your blood pressure and cholesterol.Does fasting burn belly fat? ›
Intermittent fasting is a convenient way to lose weight without counting calories. Many studies show that it can help you lose weight and belly fat.Is eating in 10 minutes too fast? ›
Your meal should take about 20 to 30 minutes. If you're gobbling up your food in 5 to 10 minutes, you're likely to experience indigestion and risk overeating. While you don't need to chew each bite 50 times, try taking a breath or putting down your utensil between bites to help slow your eating down even more.What happens if you eat too fast? ›
Leisurely eating is better for your health, especially when it comes to digestion, weight and nutrition. When you eat too fast, you swallow more air, which can cause bloating and gas. Slowing down to properly chew your food helps to break down larger particles of food into smaller ones, aiding digestion.What food does the 2 hour rule apply to? ›
The 2 Hour/ 4 Hour Rule tells you how long freshly potentially hazardous foods*, foods like cooked meat and foods containing meat, dairy products, prepared fruits and vegetables, cooked rice and pasta, and cooked or processed foods containing eggs, can be safely held at temperatures in the danger zone; that is between ...