Fasting has been practised throughout the centuries for a variety of reasons; as a form of penitence and self-control; as a method of political protest, and as a way to achieve spiritual renewal. From an evolutionary perspective, fasting is a natural phenomenon to which humans were regularly exposed thousands of years ago, which thankfully, has been replaced by a continuous and abundant supply of food for most of us. Ironically, these days, fasting is achieving popularity as a weight loss tool and as a means to improve our health and longevity because we’re eating too much! However, anyone considering fasting should be sure to consult their doctor first… it’s not suitable for everyone, particularly those taking certain medications.

We need food to provide us with the nutrients we need to sustain life; to enable our bodies to grow, repair, and reproduce. Yet it’s well documented that the high fat, salt and sugar found in the typical Western diet that the majority of us are consuming, is contributing to many preventable diseases and early deaths. The presence of artificial light also indirectly disrupts the natural daily cycle of feeding and fasting, by enabling us to be active (and eating) for up to 24 hours a day.

So should we be fasting to ameliorate the effects of our 21st century lifestyle?

What is fasting?

Fasting is generally defined as going with little or no food for a period of anywhere from 12 hours to four weeks, and is distinct from caloric restriction (CR) whereby daily calorie intake is reduced by 20–40%, but meal frequency is maintained.

What happens to our bodies when we fast?

When we eat, the food is broken down by enzymes in our gut and eventually ends up as molecules in our bloodstream. Carbohydrates, particularly sugars and refined grains (think white flours and rice), are quickly converted into sugar (glucose), which our cells use for energy. If our cells don’t use it all, insulin, a hormone made in the pancreas, draws the sugar into our cells and stores it there as fat. When deprived of regular food such as during a fast, our insulin levels go down, all the glucose is used up, and our bodies go into a metabolic state called ketosis, which is when we start to burn off our fat stores.

Putting cells under this type of stress is good for us, in the same way that vigorous exercise puts our muscles and cardiovascular system under stress. As long as we give our body time to recover – it will grow stronger, and there is considerable similarity between how cells respond to the stress of exercise, and how they respond to fasting.

Flipping the metabolic switch

According to The Longevity Institute at the University of Southern California (USC), evidence suggests that when the body switches to ketosis, old and damaged white blood cells are allowed to die off to conserve energy. Then, when provided with food and nutrients again, the body’s stem cells restock the immune system with a fresh batch of new, healthier cells.

Additional research by the same group and others, including experts at John Hopkins University and Massachusetts Institute of Technology, suggests even more benefits including:

• An increase in the number and activity of stem cells in other areas and organs such as the brain, with the potential to protect against diseases like Alzheimer’s and Multiple Sclerosis.

• A significant reduction in inflammatory diseases such as Asthma and Rheumatoid Arthritis.

• An ability to enhance the effects of chemotherapy, and kill-off pre-cancerous cells. 

• A lowering of risk factors for cardiovascular disease, diabetes and other metabolic diseases by helping the body lose weight and shed visceral fat; the most dangerous type that collects around the midsection.

The metabolic switch is typically flipped 12 to 36 hours after the cessation of food consumption, depending on the liver glycogen content at the beginning of the fast, and on the amount of the individual’s energy expenditure/exercise during the fast. Find more information here.

Different ways to fast

Despite increasing evidence to support fasting as a means to treat disease, lose weight, and prolong life, studies show that most people will fail to complete even a three day fast due to hunger pains, lack of energy, headaches and nausea. So, it’s unlikely to be achievable for the great majority of the population of most countries. So researchers at USC looked at ways to make fasting more tolerable whilst still maintaining results, and discovered that a five-day diet plan, low in protein and calories, done every month or every other month, appears to mimic the effects of a stricter protocol.

Called a fasting mimicking diet (FMD), it involves eating 1,100 calories the first day, with half of those calories coming from vegetables and the other half from plant-based, high-fat foods like nuts and olive oil. Then 800 calories a day for the next four days - again, made up of half veggies, half healthy fats. Find more information on the diet and science behind it, in the book The Longevity Diet, by Valter Longo, Ph.D., director of USC’s Longevity Institute and developer of the FMD.

Other, less severe alternatives to a full-on fast, consist of splitting the day or week into eating and fasting periods. These are the most popular methods:

1. Time Restricted Feeding: This involves reducing the ‘eating window’ to around 8 hours a day. For example, by restricting eating to the hours between 7am and 3pm or 10am and 6pm (but definitely not in the evening before bed), allowing for a 16-hour mini-fast. Limiting food intake to the middle of the day decreases body fat, cholesterol levels, fasting glucose and insulin levels, and delivers weight loss without having to count calories. Early research suggests that it may help lower the risk of cancer and metabolic disorders as well.

2. Eat-Stop-Eat: This involves fasting for 24 hours, once or twice a week, for example by not eating from lunch one day until lunch the next day.

3. The 5:2 Diet or Alternate-Day Fasting: This involves consuming only 500 to 600 calories every other day or on two non-consecutive days of the week, but eating normally the other days.

(Larger clinical trials are necessary to investigate concerns related to the effects of the frequent but irregular changes in calorie consumption and eating pattern on circadian rhythms and the endocrine and gastrointestinal systems in methods 2 and 3).

The key to all of the above, though, is to use them as an opportunity to eat a healthier, mainly plant-based diet, and not to binge during eating hours.

Are there any risks associated with fasting?

Talk to a doctor before trying any fasting method. Regardless of the approach, it’s very important to reintroduce food gradually once the fast is finished, especially after a longer one like the FMD. The first foods should be nourishing and easy to digest, so that the body doesn’t have to expend too much energy on replenishing its nutrient stores. Small amounts of whole foods and complex carbohydrates such as fruit, vegetables, and brown rice are recommended before adding other foods. Adverse effects and even deaths have been reported during or immediately after long-term fasting of several weeks, but are not associated with the intermittent fasting regimes described in this article.

Thank you for reading this blog post. If you have any thoughts to share, or ideas for future posts, please do let me know. I would love to hear from you.