The 16:8 diet plan is one of the most popular ways to get into intermittent fasting, with big names like Jennifer Aniston and Hugh Jackman swearing by it.
Similar to the 5:2 diet plan (opens in new tab) – but not as restrictive – the 16:8 has been praised as a diet that works fast (opens in new tab). We’ve spoken to the experts to find out how it works and how you can use the diet in a healthy way, without risking extreme weight loss (opens in new tab).
Clinical nutritionist Suzie Sawyer (opens in new tab) says this style of eating is very different to most of the other diets out there, and that’s why it works. “Intermittent fasting works by increasing the period when your body has burned through the calories eaten during your last meal and begins burning fat,” she explains. “If you are someone who eats three meals a day, plus snacks, and you don’t exercise much, then every time you eat, you are running on those calories and not burning your fat stores.”
What is the 16:8 diet?
The 16:8 diet is a form of intermittent fasting where you break the day into two parts: a 16-hour fasting period and an 8-hour period where you consume all your calories – hence why it is also known as the ‘8-hour diet (opens in new tab)‘.
The 16:8 stems from the 8-Hour Diet book by author David Zinczenko (opens in new tab) and Peter Moore (opens in new tab), former editor-in-chief of Men’s Health. The two created the plan off the back of the popular 5:2 diet, with the main difference being the longer fasting time between eating sessions. This, they say, gives the body the time it needs to process food and burn away extra fat.
- View The 8-Hour Diet by David Zinczenko and Peter Moore – £6.16 | Amazon (opens in new tab)
Suzie Sawyer, founder of Nutrition Lifestyle, says, “There are no restrictions on the types or amounts of food that a person can eat during the 8-hour window. This flexibility makes the plan relatively easy to follow.”
How does the 16:8 diet work?
The 16:8 diet works on an hourly basis, so each day you eat within an 8-hour time frame and then fast for the remaining 16 hours. This works for weight loss as it “helps you eat fewer calories while boosting metabolism slightly,” says Sawyer.
She adds, “It’s a very effective tool to lose weight and visceral fat. After hours without food, the body exhausts its sugar stores and starts burning fat – sometimes referred to as ‘metabolic switching’.”
Research (opens in new tab) has shown this switch is a natural process that happens when the body runs out of energy from food. The body changes its energy source from glucose that’s stored in the liver to ketones, which are stored in fat cells. While the body is getting its energy from glucose it’s maintaining or gaining weight, but when the switch happens weight is lost.
Calorie-restricted diets like the Fast 800 (opens in new tab) work in a similar way. So what’s special about the 16:8 diet?
Unlike calorie-restricted diets, short-term intermittent fasting helps to speed up your metabolism – by as much as 14%, according to research from Johns Hopkins Weight Management Center (opens in new tab). It does this by causing a rise in norepinephrine, a stress hormone responsible for releasing fatty acids from fat cells and making larger amounts of fat available for the body to burn. The faster your metabolic rate, the more calories you’ll burn by doing basic activities like sitting down, eating and sleeping. Exercise is also encouraged during intermittent fasting, which in turn helps with hanging onto and building muscle mass – another essential way to boost your metabolism.
When can I eat on the 16:8 diet?
If you’re following the 16:8 diet, you can pick any 8-hour window to suit your day.
“The most common hours adopted for the eating period is 12pm to 8pm,” explains Tom Jenane, nutrition and fitness expert at Nature’s Health Box (opens in new tab). “The reason for this is because people aren’t normally that hungry in the morning and you don’t want to be consuming too many calories in the evening. This window allows for lunch and dinner as well as healthy snacks (opens in new tab).”
But while the choice is yours, research has identified the best time to eat breakfast, lunch and dinner (opens in new tab) for weight loss. According to a study by the University of Murcia (opens in new tab), it’s best to stick to a breakfast in the morning, as skipping the meal is linked to a higher rate of obesity. Meanwhile, a late lunch (after 3pm) can hinder weight loss in those trying to reduce fat mass, and a late dinner (within two hours before going to sleep) decreases glucose tolerance, making it easier to gain weight.
What can you eat on the 16:8 diet?
- Whole grains: Rice, oats, barley, wholegrain pasta and quinoa.
- Protein: Meat, poultry, fish, eggs, nuts and seeds.
- Fruit: Apples, bananas, berries, oranges and pears.
- Vegetables: Broccoli, spinach and other leafy greens.
- Healthy fats: Olive oil, coconut oil, avocados.
The great thing about the 16:8 diet is that you can eat anything you want, within reason, but it’s important to choose whole foods and those high in vitamins during the eating period.
“Many people fail the 16:8 diet by packing in too many calories into the 8-hour period, often trying to get some in before the 8 hours ends,” says Jenane. “You should still be following a strict diet with a complete nutritional breakdown, to ensure you are consuming a targeted number of calories, not to mention macro nutrients and ensuring you’re not consuming too much sugar.”
How much weight can you lose on the 16:8 diet?
If done so correctly, there’s a typical weight loss of around seven to 11 pounds over a ten week period, according to a review of studies by Sydney Medical School (opens in new tab). They found, on average, someone weighing 90kg would lose 5% of their body weight in 10 weeks.
But how much weight you lose on the 16:8 diet depends on eating fewer calories than you’re burning. According to a leading study by the University of Vienna (opens in new tab), this energy deficit can be achieved in many ways – but is ultimately the only method of weight loss. When you eat food, your body metabolises it to create energy used for daily activities – everything from breathing to walking around. If you have more energy than your body uses, the extra is mainly stored as fat. If you have less energy than what your body can burn, your body will turn to fat stores for energy. This is the calorie deficit.
While intermittent fasting has benefits, eating in a 8-hour period alone will not automatically mean you lose weight. The plan is just one way to achieve the deficit without having to count how many calories you burn in a day (opens in new tab). The given eating time aims to automatically restrict the amount of food you can eat, leading to weight loss.
How often should you do 16:8 intermittent fasting?
You can do anywhere from one day of intermittent 16:8 fasting to seven days a week, because, unlike other intermittent fasting diets, each day of the 16:8 works independently to the rest.
Evidence differs, however, on whether it’s healthy to do intermittent fasting all the time. While research from Queen’s Medical Centre (opens in new tab) has proven that short-term fasting boosts the metabolism, longer fasts of around three or more days can actually suppress it and slow it right down. Plus, going without food for a long period of time can lead to an increased level of cholesterol, feeling sick in the morning (opens in new tab), dehydration and spells of low blood sugar.
What are the health benefits of fasting?
1. Making weight loss easier
Intermittent fasting can change the function of hormones, cells and genes, Sawyer says. “Changes in hormone levels makes stored body fat more accessible and initiates important cellular repair processes. When you fast, insulin levels drop, and human growth hormone (HGH) increases. Your cells also initiate important cellular repair processes and change which genes they express.”
2. Lowering the risk of type 2 diabetes
Anything that reduces insulin resistance should help lower blood sugar levels and protect against type 2 diabetes, says Sawyer. “Interestingly, intermittent fasting has been shown (opens in new tab) to have major benefits for insulin resistance and can lead to an impressive reduction in blood sugar levels.”
3. Reducing stress and inflammation in the body
Sawyer adds that “Studies show intermittent fasting can reduce oxidative damage and inflammation in the body. This should have benefits against ageing and development of numerous diseases, according to a study linked with the University of Toronto (opens in new tab).”
4. Supporting brain function
Because fasting has been linked to reduced inflammation, it is also believed to improved conditions associated with inflammation – which include Parkinson’s and Alzheimer’s – as well as improving memory and brain processing.
A 2007 study (opens in new tab) found that intermittent fasting can protect against cognitive decline in Alzheimer’s disease when testing on mice, while the findings of another study (opens in new tab) suggested fasting may prove beneficial in reducing the incidence of Parkinson’s in humans.
5. Improving heart health
“Intermittent fasting can improve numerous risk factors for heart disease,” Sawyer says. “This includes blood pressure, cholesterol levels, triglycerides, and inflammatory markers.”
Though she does offer a word of caution, saying “Much of this research has been done on animals and therefore needs to be studied more in-depth in humans.”
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Suzie Sawyer is the founder of Nutrition Lifestyle. She created the company originally to inform, motivate, educate and empower people to improve their health and wellbeing through nutrition.