What is intermittent fasting and does it work for weight loss?

What is intermittent fasting?

Intermittent fasting is a diet plan where you switch between eating and not eating for extended periods.

While you fast, you cannot eat any food. You can only drink water, tea or coffee. However, some will do modified fasting where you only eat 500 - 700 calories on a fasting day.

Types of intermittent fasting

Alternate-day fasting

The first type of fasting is known as alternate-day fasting (ADF) or the Eat Stop Eat method, where you eat one day and fast the next. Some refer to these as “feast” and “fast” days.

Periodic fasting

Periodic fasting is similar to alternate-day fasting, except you do one or more days of fasting in a row. The most popular type of periodic fasting is the 5:2 diet where you fast for 2 days and eat for 5 days. There are more intense types where people fast for several days or weeks at a time.

Time-restricted feeding

The final type of intermittent fasting is time-restricted eating or feeding. It is unique compared to the others in that you pick a time window within the day when you can eat, known as a feeding window. For the rest of the day, you fast.

For example, you may choose to eat all your meals in eight hours (from 10 am - 6 pm). Then after 6 pm, you don’t eat anything for 16 hours. This is known as the 16:8 method.

What are the differences between types of intermittent fasting?

What is the warrior diet?

One offshoot of intermittent fasting is the Warrior Diet. Created by fitness specialist Ori Hofmekler, the diet is designed based on survival science. It involves 20 hours of restricted eating followed by 4 hours of overeating. However, there is little evidence to support the use of this type of intermittent fasting and registered dietitians do not recommend this diet.

How does intermittent fasting work for weight loss?

Intermittent fasting works by affecting your metabolism.

The average person consumes 3 meals a day with snacks in between throughout their waking hours. This means that the body doesn’t have a chance to burn off the calories and, instead, fat builds up.

However, when you fast, you do something that Mark Mattson (PhD) of John Hopkins School of Medicine calls “metabolic switching”. Simply, fasting gives your body more time to burn through all the calories you consumed. This forces the body to switch to burning fat as a source of energy.

It also helps you naturally reduce your calorie intake. You’re less likely to snack or overeat because your feeding times are restricted.

What are the best foods to eat on an intermittent fasting diet?

While the emphasis is on when you eat rather than what you eat, you still need to eat a balanced and healthy diet. You also must choose your foods wisely during your feeding times to maximise the nutrients you get in a limited time.

In general, you should aim to eat a good amount of all the food groups whilst reducing your sugar, saturated fat and salt intake.

What are the benefits of intermittent fasting?

The main benefit of intermittent fasting is weight and body fat loss. This includes the harmful visceral fat that lines the organs and causes serious health problems.

One review of 40 studies Trusted source ScienceDirect Peer-reviewed Journals Multidisciplinary Research Go to source found that the average weight loss from this diet was around 7 - 11lbs in 10 weeks. A more recent review in 2020 looked at 27 studies Trusted source National Center for Biotechnology Information (NCBI) Government Source Biomedical Research and Literature Go to source in overweight and obese patients. They found participants lost up to 13% of their original body weight.

10 weeks of intermittent fasting could result in up to an 11lb weight loss.

Other research into the diet has found it can have additional health benefits, such as lowering your cancer risk Trusted source Oxford Academic Peer-reviewed Journals Multidisciplinary Research Go to source and improving your brain health. The most researched of these benefits are for the cardiovascular and metabolic systems.

Improves heart health

Heart disease is one of the most common and severe complications of being overweight. There is some evidence Trusted source Oxford Academic Peer-reviewed Journals Multidisciplinary Research Go to source that intermittent fasting can help improve your cardiovascular health.

There are several risk factors for heart disease, such as high blood pressure, high cholesterol and high blood sugar. Tackling these issues can dramatically reduce your risk of heart problems.

One research paper Trusted source Oxford Academic Peer-reviewed Journals Multidisciplinary Research Go to source reviewed the effects of intermittent fasting on lipid levels in the blood. Across the types of intermittent fasting, they found:

• Alternate-day fasting trials resulted in a 10-21% reduction in total cholesterol and a 14-42% reduction in triglycerides.
• Periodic fasting trials resulted in an average 5-20% reduction in total cholesterol and a 17-50% reduction in triglycerides.

They also saw significant reductions in body weight and body fat.

In terms of blood pressure, one study Trusted source National Center for Biotechnology Information (NCBI) Government Source Biomedical Research and Literature Go to source found a significant reduction in blood pressure among the 1422 participants, with none falling to a lower-than-normal level.

Lowers the risk of type 2 diabetes

Another well-attested benefit of fasting is it can reduce insulin resistance caused by high blood sugar levels, the cause of type 2 diabetes.

A build-up of fatty tissue can lead to insulin resistance from weight gain. However, through fasting, the calorie restriction and metabolic switch reduce fat tissue and therefore improve insulin resistance. Fasting has also been found to increase insulin levels, which allows for better blood sugar control.

A 2019 study Trusted source PubMed Government Source Database of Biomedical Research Go to source compared blood sugar control in those doing intermittent fasting compared to those who weren’t. They found that the diet resulted in a significant drop in blood sugar levels as well as BMI levels.

Caution: this diet is not a treatment for type 2 diabetes. Do not use this diet without consulting your doctor first.

What are the disadvantages of intermittent fasting?

There’s no denying that intermittent fasting could have some health benefits. However, despite its popularity, it is a difficult diet. It’s not suitable for everyone and, in some cases, could be harmful.

Disadvantages of intermittent fasting
Digestive issues	Headaches & lightheadedness	Feeling hungry
Low energy	Dehydration	Disordered eating

If you’re prone to or worried about these side effects, intermittent fasting may not be a good option.

Is intermittent fasting safe?

If you have any medical conditions or take any medications, do not do any form of intermittent fasting without consulting a healthcare professional. This diet could make your health worse.

Do not do this diet without advice from your doctor if you:

• have an eating disorder
• have diabetes or another blood sugar problem
• take blood pressure medicines
• have or have a history of heart disease
• are pregnant or breastfeeding
• have a bowel problem like Crohn’s disease

If you have another health condition not listed above, you should always consult your doctor first.

Tips for intermittent fasting

Creating an intermittent fasting plan is difficult, especially without the assistance of a dietitian. So, here are 5 simple tips for beginners.

1. Stay hydrated - you must stay hydrated to be safe whilst fasting, but it can also curb your appetite during your fasts.
2. Start slow - try a low-calorie fast rather than a complete fast.
3. Plan - try to plan distractions on fasting days to avoid thinking about food, such as going out, seeing people or doing an activity.
4. Choose the right foods - eating nutrient-dense foods during your fasts will help you get the most out of your calorie limit.
5. Use a fasting app - it will help you keep on top of your fast, especially if you do time-restricted fasting.

Main takeaways

In conclusion, intermittent fasting can be a great way to lose weight and improve your health. However, it’s not suitable for everyone and if you have any concerns, you should contact your doctor or dietitian before trying the diet.