How is 16:8 different to the 5:2 diet?

What is the 16:8 diet?

Part-day fasting, otherwise known as time-restricted feeding or 16:8, is generally the most user-friendly and sustainable method of intermittent fasting. Simply put, you fast for a certain number of hours (16) each day, and then follow your normal diet for the balance of the day (eight hours). This approach is very popular because there’s no need to count calories, watch your portion sizes, feel deprived or restricted or miss out on social occasions. Of all the fasting methods, the compliance rate is highest on 16:8. This is the method people are most able to stick to in the long term.

Exactly when you fast and eat on a part-day fasting day is up to you. Choose an eight-hour window that’s best for you to eat in or, perhaps more importantly, choose a 16-hour window of time that works best for you to fast in.

Option one:

Eat breakfast and fast from 3pm

This will be ideal for people who rely on breakfast to kick-start their day, and also for singles who don’t have to eat dinner with a family or partner at set times. This option is also great for people working long hours who typically turn to toast or takeaways for their dinner.

Option two: Brunch and an early dinner

This option is ideal for those who can skip breakfast but can’t quite get through to lunchtime without eating. It’s also great for people who are able to take a break mid-morning or eat at their desk, as well as parents who like to eat dinner early with their kids.

Option three: Fast until lunchtime and eat a later dinner

Ideal for chronic breakfast skippers, or those who can easily go to lunchtime without eating. It also suits those who race into work late and grab pastries or other less healthy breakfast options on the way. It’s great for corporate or shift workers who tend to eat dinner late.

What can I eat on 16:8?

In a nutshell, you don’t need to be in ‘diet’ mode. Unlike a traditional caloriecontrolled diet, you need to think more about foods you DO need to eat in order to meet your nutritional requirements, rather than what you should be eating. This is really important, particularly when you’re limiting your eating day and potentially missing one or two meals or snacks where you’d normally get certain nutrients.

Here’s a common scenario I see with morning fasters. Breakfast is a meal that often provides two of our daily dairy serves; these might be in the form of a latte and milk with a bowl of cereal. But if a person begins to fast in the morning and skips this meal, they may not meet their calcium requirements. So it’s essential they find other ways to include that dairy in their eating window. Full-day fasting (also known as 5:2 or alternate-day fasting), where a quarter of your daily calories are consumed over a full day, has become hugely popular, achieving weight-loss results where many other traditional diets have failed.

Part-day fasting needs to be done on most days, whereas full-day fasting need only be done on one, two or three days a week. Another difference is that full-day fasting requires very specific calorie counting, but only on fasting days. Unlike part-day fasting, you can eat at any point during a full-day fast, but the total calories consumed over the fasting day need to stay within 500 calories for women and 600 calories for men.

It’s important to note that eating only a quarter of your daily calories can be a little hard going for some people, and consequently, compliance rates can be low and ‘cheating’ is common. Some people also report that they find it can impact their daily functioning and work productivity.

Why 16:8 works

It’s not uncommon for people, whether on a diet or not, to start eating or drinking early in the morning and still be nibbling late into the night. But research suggests that eating for more than 15 hours of the day is associated with metabolic problems. This not only leads to weight gain, it can also impair the functioning of our cells and accelerate the ageing process.

Fasting, on the other hand, gives our body, specifically the energy powerhouses (aka mitochondria) in our cells, a break from processing constantly. When we eat, food moves from our stomach to our small intestine, where it begins the complex job of sending off nutrients in different directions. The energy or calories we consume gets used right then and there to fuel our daily functions of breathing, walking, digesting, even thinking!

Some fuel will also be stored as a quick-access source of energy in the form of glycogen in our muscle and liver cells. Then if we’ve eaten a high-calorie meal or simply consumed more energy than our body needs and there’s excess energy left over, we store that as fat, causing us to gain weight. Generally, though, if we eat only as much energy as our body requires, our weight will stay the same.

If it’s been some time since we last ate and the glucose levels in our blood have dropped, our body then needs to access more fuel. First, it turns to the stored ‘quick-access’ energy from glycogen. Once those glycogen stores have been depleted, our bodies switch into ‘fat-burning’ mode, breaking down mostly fat stores but also some body protein (muscle) as well.

Depending on your level of physical activity, humans will shift into this fat-burning mode after as little as 12 hours of fasting. In other words, fasting and restricting our energy intake periodically allows our body to access and break down stored fat, and this leads to fat loss.