Fast facts: the ins and outs of fasting
Thinking about giving fasting a try? Here’s what you need to know beforehand. Spoiler alert: there is a way you can eat to enjoy the benefits typically achieved by fasting. Article first published in Nourish Magazine.
Rewinding to just over a decade ago, I had the experience of completing a three-month medical school placement at TrueNorth Health Center in California, under the supervision of internationally renowned physician and nutrition expert Dr Michael Klaper. TrueNorth offers a residential program based on a wholefood, plant-based diet, free from refined salt, oil, and sugar. It is also one of the only places in the world that offers medically supervised water-only fasting. Before undertaking my training at the centre, I knew nothing about fasting and since then, there has been an explosion of interest in this area. If this is something you are considering, here’s what you need to know as a starting point.
What you do eat matters more than any fast
Let’s get something straight before we consider any type of fast. Dr Klaper says, “More important than the fast is the food you eat day after day, month after month, year after year.” And the eating pattern the doctors at TrueNorth recommend before, and especially after a fast, is unanimously a diet of whole plant foods.
More important than the fast is the food you eat day after day, month after month, year after year
In fact, virtually every benefit ascribed to fasting – better metabolic health (improved insulin sensitivity and lower cholesterol), weight loss, lowered risk of cancer, reduced inflammation, and increased longevity – is also a benefit demonstrably experienced by those consuming a plant-based diet with whole and unprocessed foods as the foundation. There are good reasons for this, including that wholefood, plant-based eating is already naturally lower in energy density while still being satiating and nutrient dense. Therefore, to some extent this can mimic the caloric restriction a fast may aim to achieve. This type of eating pattern also excludes animal protein, which we know increases insulin-like growth factor 1 (IGF-1). A reduction in IGF-1 is touted as one of the most important effects of fasting, and some findings even imply that it is the reduction of protein intake that is most important to achieve this effect.
Invariably, people who participate in fasting studies do not all eat a healthy, low-fat, wholefood, plant-based diet. So, these studies don’t necessarily tell us whether fasting can add to the health benefits already gained when you eat this way. Longevity researcher Dr Valter Longo has become world-famous for his fasting trials and one of his most interesting findings is that the people who benefit most from his fasts are those who are the unhealthiest in the first place. While the effects of fasting will vary from individual to individual, you can be certain that any effect is ultimately less important than what you eat day to day on an ongoing basis. Just as you can’t out-exercise an unhealthy diet, you can’t out-fast one either.
Is there any benefit to fasting?
A fast is simply a period of abstaining from food and, in its purest form, would involve consuming only water for a specified time period. We carry fuel reserves that enable us to survive for significant periods of time between meals. About four to six hours after a meal, your body will have either used or stored the energy provided. In the absence of new glucose (energy) from food, your liver starts increasing production of substances called ketones to help keep your brain fuelled. As your body uses more of its stored glucose, it becomes more reliant on ketones, until at some point (usually around 16 hours after the last meal) it can be said to be in ketosis. This means your body is primarily operating on stored fat and ketone bodies.
Ketones signal a switch in your body’s metabolism. While in the ‘fed’ state, your metabolism favours growth and flexibility, whereas a ‘fasted’ state is characterised by an increased defence against stressors and repair of damage. Therefore, temporary forays into the fasted state are thought to slow ageing and be beneficial for health through numerous mechanisms. For example, a cellular cleaning process known as autophagy ramps up, enabling the body to clean out damaged and old cells, ultimately replacing them with newer, healthier ones.
However, there’s something important to understand about this process. It is the regular switching between the fed and fasted states that seems to be most natural and beneficial. Prolonged periods spent in either of these states at the exclusion of the other are likely to be suboptimal (and yes, this includes the keto diet).
Types of fasts you might consider
Because most of us live in an environment of calorie excess where food is available 24/7, we may only ever experience a fast when asleep. And many of the beneficial processes of fasting start up within hours, not days, of us going without food. In recent years, evidence has been mounting around the benefits of either intermittent fasting or an adaptation of periodic fasting that allows food. Let’s look at the most common variations:
The 16/8 Method
This form of intermittent fasting uses time-restricted feeding, where eating is limited to an 8-hour window during the day. For example, if the first meal is at 11 am, the last meal for the day would be finished by 7 pm. While most people achieve this by skipping breakfast, the optimal option metabolically would be to skip dinner instead.
The 5:2 Diet
In this variation of periodic fasting, calories are restricted on two non-adjacent days of the week, where only 800 calories are consumed. On the other five days, you eat as you normally would. This isn’t really an actual fast and is therefore presumably less likely to result in the benefits associated with fasting, depending somewhat on meal timing and composition.
Eat Stop Eat Fasting
This is a type of intermittent fasting that involves not eating for 24 hours, once or twice a week. During the 24-hour fasts, usually between dinner on one day to dinner on the next day, only water is consumed. This should result in at least six to eight hours of ketosis for most people. I would advise against anything more than gentle exercise during this period if you try this.
Fasting Mimicking Diet
This is a restricted-eating program where specific plant-based foods and supplements provided in a pack are consumed for five consecutive days, no more than once a month. On the first day, about 1,100 calories are consumed, dropping to 725 calories on days two through five. While some eating continues during the fasting period, the diet is designed to trick your cells into thinking they aren’t being fed.
To fast or not to fast?
Australian longevity guru Dr David Sinclair suggests “almost any periodic fasting diet that does not result in malnutrition is likely to put your longevity genes to work in ways that will result in a longer, healthier life.” While fasting may benefit many of us, it won’t be right for everyone, depending on personal and medical histories. Those with a history of disordered eating or other risk factors should be particularly cautious. Always consult a health professional who is trained and has experience with fasting if in any doubt. And, because fasting does place a strain upon the body, it is a practice that we are best to ease into – especially females, whose bodies can be more sensitive to changes in energy intake and timing of this.
While fasting may benefit many of us, it won’t be right for everyone.
However, some form of time-restricted eating can be possible and helpful for most of us. If the methods discussed previously seem too extreme for you, you can instead aim to eat within a 12-hour window each day – from ‘sun up to sun down’. Try to have a bigger breakfast and a smaller dinner. Our insulin sensitivity is greatest in the morning, and we are more likely to store calories consumed later in the day, which can also affect our sleep.
For those who’d like to try something closer to a traditional fast, the fasting mimicking diet would be a better option than a water-only fast for most. If you have specific medical issues that you believe would be best addressed by a water-only fast, then medically supervised is the only way to go. Find a reputable and established clinic like the one I trained at, TrueNorth, to support you.
Personally, I tend to keep my eating within a window of 10–12 hours each day. I regularly ‘fast’ one day a week, consuming only water. I might try Dr Longo’s fasting-mimicking diet once or twice a year, though I don’t particularly like the idea of stopping or restricting my exercise, work, and social life to complete it.
After all, there’s something to be said for quality of life! And a whole food, plant-based eating pattern provides the best of both worlds – enjoying loads of healthful whole, plant foods while also reaping numerous benefits not dissimilar to those provided by fasting.