Referred to as the “original human diet”, fasting has become one of the hottest topics in health and wellness discussions. Is it all just clever marketing or are there REAL long-term benefits?

So much has been written about fasting and various fasting-based diets, I wanted to look into some science-backed info. Is there research-backed evidence of the health benefit claims? Are fasting-based diets really effective as a sustainable weight loss tool? I’ve also come across a number of different versions – what do they actually entail?

This post is not about providing advice – it’s about sharing some introductory and hopefully helpful info about fasting diets. If you decide it’s something you’d like to look into further, you should get guidance from a healthcare professional before embarking on a fasting programme.



There have been a number of studies on the effects of fasting on health and longevity.  Interestingly, the research is showing that significant calorie reduction over specific periods of time may actually improve long-term health.  I’m focusing on 3 of the more common fasting-based diets I’ve come across. Time-restricted feeding (TRF), intermittent calorie restriction, and periodic fasting.


Time-restricted feeding (TRF)

TRF is where one limits calorie intake to a certain time period each day. This is usually somewhere between 8 and 12 hours a day. So, for e.g. you would only eat between 10am and 6pm or 6am and 6pm, which means you would fast overnight for 16 or 12 hours respectively each day. TRF extends beyond the usual focus of a diet on “what” and “how much” you eat. It looks at a 3rd component of “when” you eat.


How it works

Circadian Rhythm Diet

TRF is based on research around circadian rhythms (your 24-hour biological clock), and how sleep patterns, physical activity and eating affect them. This is why it’s also sometimes referred to as “Circadian Rhythm Fasting”.  Circadian rhythms optimise health by coordinating cellular function, tissue function, and behavior.

The digestive system works in a particular sequence throughout the day. It turns on when we break our overnight fast and first consume calories each day. Once the food has moved through the digestive system and has been processed by all the necessary organs, everything goes on “stand-by” until next we eat.  After our last meal of the day, our body goes into an essential “maintenance” process to repair and replenish. If you throw in a late dinner or midnight snack, you throw the entire process and system off.


What has the study shown?

Eating during consistent time periods each day helps keep the biological rhythms in sync and functioning at peak efficiency. There is some good scientific evidence suggesting that Circadian Rhythm Fasting, when combined with a healthy diet and lifestyle, can be a particularly effective approach to weight loss, especially for people at risk for diabetes.  According to the research, a sustained fasting-feeding cycle with at least 12 hours of fasting overnight is optimal for good health.

What’s optimal for you depends on your goals and what works practically for you. The research shows that in order to improve overall health, restricting eating to 8-9 hours EARLIER in the day is optimal to begin with but that moving to 10-12 hours may be more practical in the long term. It’s always advisable to start off slowly and consult a medical practitioner, especially if you’re on any meds or have any pre-existing health concerns.

Click here to read more about TRF.


Intermittent calorie restriction

As the name implies, this means reducing the calories consumed in a day and is also sometimes referred to as “intermittent fasting” The research focused on the currently popular 5:2 diet or “Fast” diet where one follows a calorie-restricted, low-carb diet for 2 days a week.

It’s interesting to note that the research in this case was conducted by Dr. Michelle Harvie, a research dietician and breast cancer researcher whose work is focused primarily on weight loss to help reduce the risk of breast cancer.


How it works

Dr. Harvie wanted to find what is effectively a “short, intermittent, intensive therapy” and practical way to get people to lose weight by consuming fewer calories. It requires cutting calories to about a quarter of your daily requirement for 2 days, about 500 calories for women, and then eating 2000 calories “normally” but healthily, for the next 5 days.


What has the study shown?

Short-term human studies on the 5:2 diet have shown that it is a practical and potentially effective option for weight loss which in turn, can help prevent chronic diseases associated with ageing. Longer-term studies however are still in the works.

If you’re struggling to lose some extra weight, or just looking for a way to kick-start a health journey, a 5:2 diet may be a great way to reset your body and make you think more carefully about how you eat. If this appeals to you, you can find out more about the 5:2 diet here.


Periodic fasting and Fasting Mimicking Diet (FMD)

This is a more “extreme” version of fasting that requires one to limit calories for between 3 to 5 days. The aim is to deplete glycogen stores at a cellular level and begin ketogenesis. More simply put, this means that the body has used up all its regular energy stores from food, and starts breaking down fat for energy.


How it works

Basically, the researcher, Dr.Longo  says it’s about breaking down and rebuilding. After three to five days of ketosis, you return to a normal range of calories again and the cells receive glucose to build back up, fresh and rejuvenated. “It’s much more about the feeding than it is about the restriction,” Longo says. “This combination can cause the destruction of damaged cells and replace them with functional ones.”

This doesn’t mean you have to only drink water for 3-5 days. Dr. Longo has developed a “fasting mimicking diet” (FMD). It’s a five-day program during which time one limits total calorie intake to between 770 and 1100 per day. This helps with enduring the mental and physical rigors of fasting by providing nutrients to the body without stopping the fasting process at the cellular level.


What has the study shown?

In Longo’s human study, the FMD group experienced a number of health benefits. They showed significant improvement in body weight, waist circumference and BMI as well as absolute total body fat. They also showed improvement in risk factors for aging and disease, including systolic blood pressure and insulin-like growth factor.

Periodic fasting would seem to promise the greatest potential health benefits. However, it is not for the faint-hearted and can be grueling and uncomfortable. It is not adviseable to undertake periodic fasting or FMD without sound medical guidance.

You can read more about Dr.Longo and his research here.



If you’re interested in learning more, I’d recommend you watch this documentary, Fasting – The Movie. You can check out the official trailer below.



(RELATED POST: Why keeping a food diary is a good idea)

Close My Cart
Close Wishlist
Recently Viewed Close