Not so fast

Tracy Venter

A closer look at the intermittent fasting trend taking the health world by storm.

There’s a new dietary trend in town, and it has less to do with what you eat than when you eat. From Hollywood celebrities to Silicon Valley executives, it appears everyone in the know is jumping on the intermittent fasting (IF) bandwagon.

There are various approaches to the diet, but at its core, the idea is to severely restrict your food intake (fast) on some days, and eat normally on other days. When done regularly, this approach is said to improve health, focus, and productivity, as well as promote weight loss. But what does the medical research say about it?

Throughout medical history, fasting has been used to assist patients in disease recovery and to improve key biomarkers of health (e.g. insulin levels, blood pressure, cholesterol). The practice is also prominent in many of the world’s major religions. In the modern world, we have food available at our fingertips, and rather than worrying about where to find their next meal, many people struggle to stop themselves from overeating. This makes the concept of fasting – willingly abstaining from food for a set period of time – seem daunting, or even downright unnecessary.

Proponents of IF do not promote extended periods of food deprivation, but encourage shorter, regular bursts of fasting as a lifestyle.

Typically, there are three approaches. The first is alternate day fasting. This involves consuming no calories on fasting days, and countering this with unrestricted calorie consumption on non-fasting (“feast”) days.

The second approach – modified fasting – allows for food intake equal to 20 to 25% of daily energy needs on fasting days, and normal food intake on feasting days.

The most popular approach is the 5:2 diet, which recommends five days of normal calorie intake per week, coupled with two days of reduced calorie consumption, not exceeding 25% of energy intake requirements. This equates to roughly 2 000 kj for women and 2 400 kj for men on fasting days. This approach involves selecting an eight-hour window period every day in which to eat – for example from 11am to 7pm – to allow your body to fast for 16 hours a day.

A large amount of research has been conducted on the effects of IF on health using animal models. In comparison, the research on humans to date is scarce, but on the increase.

Studies found that regular fasting and/or calorie restriction may produce a range of beneficial health outcomes, including decreased insulin sensitivity; reduced inflammation; weight loss and weight regulation; reduced obesity risk; symptom improvements for various autoimmune diseases including rheumatoid arthritis and multiple sclerosis, heart disease, cancer, diabetes, Alzheimer’s, and Parkinson’s; improved sleep quality; improved brain health, and increased longevity. In human studies, research shows that the 5:2 diet aids in weight loss, and that intermittent fasting in general has positive outcomes on participants’ mood and self-confidence, as well as marked improvements in fasting insulin and inflammatory markers.

The reasons behind the health benefits are varied, but can be partly explained through considering circadian rhythms. In nature, every animal operates according to a daily cycle that influences waking, eating, sleeping, and cellular repair processes. Human rhythms have adapted to sync with the sun: we wake up when it is light, and start feeling tired when it is dark, bearing in mind that our ancestors did not have artificial lighting to interfere with this rhythm.

Our bodies metabolise glucose more effectively during the morning, and throughout the day different appetite-regulating hormones are triggered. When we eat too late at night, our body isn’t at the optimal stage in the circadian rhythm to effectively process the food. This leads to reduced sleep quality, and a good night’s sleep is vital in controlling appetite-regulating hormones.

Additionally, the body expends a large amount of energy digesting food. If we constantly eat, the body cannot free up energy at critical points throughout the day to do essential healing and maintenance, fight inflammation and maintain optimal health.

Of course, not everybody should throw caution to the wind and embrace IF as a lifestyle. It is important to take your physical and mental health into account, as well as factors such as age, gender, and lifestyle.

Pregnant and breastfeeding women, people on medications that must be consumed with food, the elderly, children, and anybody with a diagnosed medical condition should first seek guidance from a trained medical professional before engaging in IF.

People with a history of eating disorders should also be cautious, because the “fast” and “feast” approach could exacerbate obsessive tendencies and the need for control over food. Additionally, in susceptible individuals, IF can also lead to an unhealthy obsession over meal planning and constantly thinking about the next meal. Fasting also places the body in a mild “stress state”, which elevates cortisol levels and may lead to muscle breakdown and fat storage in women as a result.

As a final piece of advice, if you are considering an IF diet, always remember that food quality is key. The days that you do take in nutrients are crucial, as your body needs nutrients for every cellular function.

This is why cutting out refined, processed foods, and only eating – organic when possible – whole-foods is essential for long term success on an IF diet.