The 16:8 diet

The 16:8 diet is a form of intermittent fasting or time-restricted eating. The numbers in the ratio stand for 16 and 8 hours (of fasting and eating, respectively).

Intermittent fasting vs time-restricted feeding

These days, the term “intermittent fasting”, is being thrown around all over the place. Prof Valter Longo is the opinion that we need to stop using term “intermittent fasting” because it’s being used to talk about different protocols that have different effects on health (minute 1:01 in the video below).

Simply put, fasting = not eating. If you do it intermittently (i.e. not all the time), you are intermittent fasting. Humans, and all creatures, have fasted since the beginning of time. It can be argued that intermittent fasting is what our bodies are hard-wired to expect.

Time-restricted feeding is a specific type of intermittent fasting that happens every day (in contrast, intermittent fasting can be done, for example, once a week). The focus here is placed on the number of hours in which eating is “permitted”, i.e. 8 in the case of the 16:8 diet.

In some forms of fasting and all forms of time-restricted feeding, the idea is not alter the quantity or quality of food, but to consume it within a fixed window of time.

One more nuance: circadian rhythms

Circadian rhythm is what underlies any biological 24-hour cycle. Many organisms, including our own human cells, function according to a circadian rhythm that is influenced by the natural light/dark cycle and feeding/fasting periods. During the fasting periods, the body has an opportunity to repair damaged cells, proteins, etc. (2, 3).

Unfortunately, our modern lifestyles with 24/7 artificial light stimulation, disrupted sleep and eating patterns interrupt our body’s natural processes, predisposing us to obesity, diabetes, cardiovascular disease, etc. Hence, the aim of time-restricted feeding is to re-establish the body’s innate circadian rhythms (2, 3).

Prof Satchin Panda is dedicated to the study of circadian rhythms and health.

Benefits of fasting

The health benefits of fasting have been well documented thanks to large observational studies of populations who practice religious fasting. There have been also numerous studies in mice and other creatures that have given insight into the physiology of fasting, due to the fact that several cellular processes are conserved across species (2, 3).

Fasting promotes ketogenesis, increased cellular stress resistance, breakdown of fats (lipolysis) and cell destruction (autophagy). Clinical applications include the treatment of neurodegenerative, metabolic and inflammatory diseases, aging and certain types of cancer (particularly to reduce side-effects of chemotherapy) (1). Fasting may also help lower blood pressure and body fat (2).

Does the 16:8 diet work for weight loss and health?

A recent paper reported on a 12-week pilot study with 23 obese sedentary adults who followed a 16:8 diet. Subjects were allowed to eat from 10am to 6pm and their results were compared to matched subjects from another weight loss study. The experimental group more lost body weight and systolic blood pressure than the control group, but no relative fat mass, lean mass, diastolic blood pressure, heart rate, cholesterol, triglycerides, glucose, insulin nor homocysteine (a risk factor for cardiovascular disease). The authors of the paper acknowledge that alternate day fasting may be more effective for weight loss than time-restricted feeding (4).

On the flip side, an 8-week study with 34 lean young adult subjects explored the effects of combining a 16:8 diet with exercise. All subjects had been lifting weights for at least 5 years and followed a classic bodybuilding protocol 3 times per week. The time-restricted group ate between 1pm and 8pm and lost more of the following: fat mass, total testosterone, IGF-1 (but maintained fat-free mass), blood glucose, insulin, triglycerides, TNF-α and IL-1β (pro-inflammatory cytokines) (5).

Any fasting protocol may have detrimental side effects, so consult with your doctor or dietitian before trying the 16:8 diet, especially if you have health challenges or risk factors.

In the media

The 16:8 hour in the media was popularised under the name of 8 hour diet by American publisher David Zinczenko of Men’s Health back in 2012.

My experience with fasting

I don’t follow a structured fasting protocol but I do try to do some sort of fasting at least once a week. Sometimes it’s a 24 hour fast, sometimes it’s a protein fast (which triggers autophagy without requiring an actual fast), sometimes it’s a 8-12 hour time-restricted feeding period. The day and length depend on what else I have going on, i.e. training and social events. I try to implement fasting on recovery days, in which I do minimal physical activity (such as stretching, yoga or sprints). I learned the hard way: I tried fasting on a day I did clean heavy singles and I almost fainted.

References

1. Longo VD and Mattson MP. Fasting: Molecular Mechanisms and Clinical Applications. Cell Metab. 2014 February 4; 19(2): 181–192.
2. Longo VD and Panda S. Fasting, circadian rhythms, and time restricted feeding in healthy lifespan. Cell Metab. 2016 June 14; 23(6): 1048–1059.
3. Melkani GC and Panda S. Time-restricted feeding for prevention and treatment of cardiometabolic disorders. J Physiol. 2017 Jun 15;595(12):3691-3700.
4. Gabela K et al. Effects of 8-hour time restricted feeding on body weight and metabolic disease risk factors in obese adults: A pilot study. Nutr Healthy Aging. 2018 Jun 15;4(4):345-353.
5. Moro T et al. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. J Transl Med (2016) 14:290.

[Photo by petradr on Unsplash]

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