For weight loss without GLP-1 drugs, surgery or calorie counting, intermittent fasting has become a trendy option to try. Even Elon Musk says he’s been fasting periodically and some members of our Start TODAY group credit the eating style with helping them lose weight.
There are several ways to do it, but the 16:8 plan is a popular option. It’s a version of time-restricted eating, which divides the day into periods of fasting and eating.
Here is what you need to know about the plan:
What is 16:8 intermittent fasting?
Intermittent fasting means only eating during a certain window of time each day or fasting on a regular weekly schedule. The 16:8 intermittent fasting plan means you fast for 16 hours of the day and eat for eight.
It’s not a diet, so unless you have individual dietary restrictions, you can eat whatever you want within the 8-hour time frame. But the plan will work best for weight loss if you are already making smart, nutrient-rich choices, says NBC News health and nutrition editor Madelyn Fernstrom.
For some people, restricting the amount of time they eat in a day naturally limits the number of calories they consume and therefore contributes to weight loss.
It might be better referred to as “intermittent eating,” because it’s not about deprivation, but rather about “boosting mindful eating and a new relationship with food,” Fernstrom adds.
Is 16:8 fasting good for weight loss?
The results are mixed.
A small 2018 study found people with obesity who followed the 16:8 fasting regimen for three months lost almost 3% of their body weight and lowered their blood pressure without feeling hungry or deprived.
The participants ended up eating 350 fewer calories a day compared to a control group simply because they couldn’t squeeze in their normal food intake between 10 a.m. to 6 p.m., the prescribed eating window in the study, co-author Krista Varady, a professor of nutrition at the University of Illinois, Chicago, tells TODAY.com. She has been studying fasting for 20 years.
Varady’s latest study, published in June 2023, showed time-restricted eating without calorie counting was as effective as limiting calories and tracking them for weight loss. For the trial, people with obesity were asked to either eat only between noon and 8 p.m. or eat whenever they wanted, but count calories and reduce the total they normally ate by 25%. They followed those routines for six months.
Both groups generally maintained the weight loss after their diets ended and lost 5% of their body weight over the course of a year, Varady told NBC News.
A 2020 systematic review of 27 studies that involved different kinds of intermittent fasting, including the 16:8 plan, found participants lost between 0.8% to 13.0% of their initial weight with no serious adverse events. The authors concluded Intermittent fasting “shows promise” for the treatment of obesity.
But research presented at the American Heart Association’s Scientific Sessions in 2020 found obese adults who ate most of their calories by 1 p.m. for three months didn’t lose more weight than those who followed a more typical eating pattern, including eating a big meal after 5 p.m.
“The bottom line is that how many calories you take in is really much more important than when you eat, and that when you eat probably doesn’t impact your weight,” Dr. Nisa Maruthur, the lead author, a primary care physician and associate professor of medicine at Johns Hopkins University in Baltimore, previously told TODAY.com.
And the results of a 2023 study on the timing of meals, published in the Journal of the American Heart Association, “did not support the use of time‐restricted eating as a strategy for long‐term weight loss,” researchers wrote. The timing of meals was less important than the amount of food a person ate, they noted.
Is 16:8 fasting healthy?
Weight loss or not, there appear to be health benefits to intermittent fasting.
It may protect the heart by controlling inflammation, according to the American Heart Association.
“The idea is that if you eat all of your calories within a relatively fixed time window… it’s better because it allows your body to do this metabolic catch-up during a fasting state when you’re not eating,” Dr. Susan Cheng, a professor of cardiology and the director of public health research in the Smidt Heart Institute at Cedars-Sinai in Los Angeles, tells TODAY.com. “I would say the jury is still out, but there is a lot of compelling evidence to suggest that is going to be favorable for cardiometabolic health.”
Studies and clinical trials suggest intermittent fasting has “broad-spectrum benefits” for health problems including obesity, diabetes, heart disease, cancer and neurologic disorders, according to a review of research in humans and animals published in 2019 in The New England Journal of Medicine.
The powerful health effects appear to come from the body flipping a “metabolic switch” during fasting — or shifting away from using sugar as its main source of energy and instead converting fat for fuel when a person’s stomach is empty.
But most people still eat throughout the day and miss out on the health benefits of a fasting window, said lead author Mark Mattson, adjunct professor of neuroscience at the Johns Hopkins University School of Medicine.
Does 16:8 fasting work for people with Type 2 diabetes?
Eating only within an eight-hour window can help people with Type 2 diabetes lose weight and manage their blood sugar, according to a study published in JAMA Network Open in October 2023.
The clinical trial involved 75 adults with Type 2 diabetes and obesity who were randomly divided into three groups for six months. One group could eat whatever they wanted and how much they wanted, but only between noon and 8 p.m. The second group was instructed to eat 25% fewer calories than normal, and the rest stuck to their usual eating routine.
The participants’ weight and blood sugar levels were measured at baseline, and then regularly throughout the six-month trial.
“We found that the fasting group lost twice as much weight as standard care (daily calorie counting), but both groups improved HbA1c, a key diabetes risk parameter, similarly,” Varady, a co-author of the study, tells TODAY.com.
HbA1c measures a person’s average blood sugar levels over the past three months. It fell about 0.7% for both groups. But when it came to weight, the fasting group lost about 10 pounds over six months on average, compared to less than 6 pounds for the calorie-counting group.
Eating fewer calories is commonly prescribed as the first line of defense in Type 2 diabetes treatment, but many patients struggle with it so time-restricted eating may offer a “refreshing alternative,” the paper notes.
There were no serious adverse events reported during the trial, so the study shows intermittent fasting is safe in this population group, Varady says. But she advises people with diabetes to always check with their doctors before starting time-restricted eating.
The findings need to be confirmed by larger trials with longer follow-up, the authors note.
Intermittent fasting isn’t for people with Type 1 diabetes who take insulin because it may result in unsafe levels of hypoglycemia, or low blood sugar, during the fasting period, Mattson says.
Why some experts think intermittent fasting is better than dieting
Intermittent fasting can be easy to follow, provide daily structure and often doesn’t require any calorie counting. It also reconnects people with true, biological hunger and makes it easier to recognize fullness, so they stop eating sooner, Fernstrom notes.
Unlike many fad diets, intermittent fasting doesn’t lead to eating disorders or slow down a person’s metabolism, Varady says. She’s the co-author of a 2022 review of studies that found intermittent fasting is generally safe and produces few gastrointestinal, neurological, hormonal or metabolic adverse effects.
Varady dabbles with intermittent fasting herself, typically for a few weeks after the holidays to lose a few pounds.
How to intermittent fast:
If you’re ready to try 16:8 intermittent fasting, Varady has some tips to make sure you do it in a way that is healthy and works with your life.
Pick a time window that works for you
Experts advise picking an eating window that lets you finish your meals fairly early, such as 10 a.m. to 6 p.m. or earlier, because the body is less efficient at processing sugar as the day goes by.
In an “absolute ideal world,” people would eat breakfast, take in most of their calories during the first part of the day, have a very light dinner — if any at all — and then fast for the rest of the evening, Cheng says. She calls that potentially the best timing, but knows many people derive a psychological benefit from sitting around the table at dinner.
So it’s important to pick a window of time that works for your schedule. If you’re a very early riser, for example, it may be difficult to wait until noon to eat.
Exercise before you eat
Most people get hungry about half an hour after they finish working out and may find it too hard to stick to their plan if they can’t eat anything at all afterward, Varady notes. That’s why it’s important to exercise before you eat.
If you’re on the 16:8 plan, exercise before your eating window or make sure to finish your workout at least 90 minutes before your eating window ends for the day.
Get enough rest
Fasting for 16 hours may sound tough, but if you’re getting the recommended seven or more hours of slumber per night, you’ll be asleep for about half of it.
If you experience moments of low energy, you can try:
- Drinking black coffee. Drinking coffee can improve concentration and energy and has no calories in it, Varady says.
- Taking a deep breath. Mindfulness and a bit of meditation can go a long way in helping to restore your energy during your fasting period.
Make it a true fast and avoid snacking
Many people are used to grazing and nibbling all day long, but there’s no snacking during the fasting periods of intermittent fasting. Here are some ways to avoid getting “hangry:”
- Eat high-fiber foods, such as nuts, beans, fruits and vegetables and high-protein foods, including meat, fish, tofu or nuts, during your eating window, Varady advises. Chewing high-fiber gummies can also help.
- Drink lots of water. People tend to think they’re hungry when they are really just thirsty, Varady says.
- Go for black coffee or tea, or cinnamon or licorice herbal teas. These beverages may have appetite-suppressing effects, Varady notes.
- Watch less TV. “I know this sounds strange, but while you are watching TV, you are bombarded with dozens of ads for food. This can make you feel hungry, when in actuality, you are not hungry at all,” she says.
- Use peppermint to defuse cravings. Inhaling a peppermint scent every two hours helped people defuse cravings and eat fewer calories, a study found. The exact reasons why are unclear.
Remember, being “a little hungry” is the best thing that can happen to you, wrote Fernstrom, calling it a “true mind-body connection” that helps you recognize fullness.
Avoid drinking too much alcohol
Don’t drink any alcohol during a fasting window or a fasting day since it’s high in calories and has no nutritional value, Varady advises. During non-fasting periods, women should limit their alcohol intake to one drink a day; men shouldn’t have more than two.
3 other things you should know about intermittent fasting
Here’s more information to know before you commit. Always check with your doctor before starting a diet.
Intermittent fasting is not for everyone
Researchers say intermittent fasting is not for everyone, including:
- Children or adolescents.
- Women who are pregnant or lactating.
- People vulnerable to eating disorders.
- Individuals who are underweight (have a body mass index below 18.5).
- People over the age of 70, because fasting may exacerbate muscle wasting in this population, Varady says.
Different ways to intermittent fast
If the 16:8 plan doesn’t appeal to you, there are other ways of intermittent fasting. Some other types of intermittent fasting include:
- Alternate day fasting, which means eating nothing or very little (up to 500 calories) one day, then eating whatever you want the next, and then repeating that process.
- The 5:2 plan, which means incorporating two non-consecutive fast days into your week, then eating normally during the other days.
- One meal a day (OMAD), which is sometimes also called the 23:1 regimen because a person spends up to 23 hours a day fasting and only eats during a brief window.
It’s OK to skip breakfast
The notion that omitting a morning meal is bad for your waistline likely began with studies sponsored by cereal companies, and most of that research looked at the effects of breakfast skipping on cognition in children, Varady notes: “I’m not sure how that all got translated to body weight.”
Indeed, a 2015 study found breakfast may not be the most important meal for weight loss. Another analysis, by obesity and nutrition researcher David Allison, found there wasn’t scientific data to definitively support a link between eating breakfast and weight loss, or skipping breakfast and weight gain.