Intermittent Fasting


Now that the holiday season is a distant memory, we might all need to shake things up in the health department.


Intermittent fasting (IF) is an umbrella term for various diets that cycle between periods of food restriction (or fasting) and non-fasting. The period of restriction may be hours or whole day, and may be fluid-only or significantly reduced food intake (calorie restriction). The period of non-fasting may be a feast, normal eating, or quite mindful consumption, depending on the protocol.


The goals of intermittent fasting include not only weight loss, but disease prevention and treatment. Some people even employ therapeutic fasting in an attempt to slow the effects of ageing.


Traditional calorie restrictive (CR) diets can dramatically improve metabolic health and other markers of health and longevity. Intermittent fasting regimes (in animals) also increase longevity, and reduce the risk of CVD, metabolic dysregulation and cognitive dysfunction (Horne et al. 2015). The effects in humans, while promising, are less well researched.


As the food restriction of IF is less frequent, but more intense, than CR diets, some find compliance more achievable. Therapeutic fasting is emerging as a preferred and effective alternative for sustained weight loss and other health outcomes.



5:2 Fasting - involves adopting a reduced calorie regimen on two (usually) non-consecutive days a week. Reducing to one-day/week fasting for maintenance.

Alternate Day Fasting - eating every other day. More restrictive than the 5:2 diet, possibly requiring greater lifestyle modifications to compensate for low energy days, and therefore, more challenging to sustain.

Time Restricted Feeding (TRF) – confines food access to an 8-12 hour window during the active phase (fasting for 12+ hours/day).  Fasting for religious reasons such as that observed by Moslems during the month of Ramadan, restricting dietary intake between sunset and sunrise, is similar to TRF.

16:8 fast - 8-hour active phase (say 10am-6pm). There is no calorie restriction, which may aid compliance. It may be useful for those who struggle to reduce daily food intake without side effects, or without inhibiting activity levels. It is also used in cancer treatment when prolonged fasting is inadvisable.


How does it work?

The mechanisms for the benefits of IF are not entirely known, but are thought to involve the body’s use of fat for energy during fasting, reducing adipose mass and resulting in small, short-term reduction in risk after each fasting episode.


Low carbohydrate/ketogenic diets rewire energy metabolism to utilise ketones as an energy source rather than glucose. Fasting for more than 12 hours also utilises fat for energy. These diets mimic many of the metabolic and anti-inflammatory properties of Calorie Restriction, including reduced blood glucose, insulin, and IGF-1, fatty acid oxidation and generation of ketones. The ketogenic diet has been used successfully in type 2 diabetes.


Nutritional stress during fasting results in cellular repair, functional optimisation and metabolic rejuvenation, impacting the aging process. Our modern-day 24hr lifestyle, through the use of artificial light and technologies, causes disruption to the natural activity-rest cycle, circadian rhythm, and natural feed-fast cycle. This can contribute to metabolic disease and my also accelerate the aging process. Shift work and sleep deprivation have been linked to predisposition to cancer, obesity and metabolic syndrome.



In humans Intermittent Fasting can have a wide range of effects on metabolic markers and risk factors for diseases, including: reducing body (& visceral) fat, blood pressure, triglycerides, LDL cholesterol particle size, LDL cholesterol, C-reactive protein; increasing insulin sensitivity, HGH (facilitating lipolysis and fatty acid release for energy), red blood cell count. There are no clinically significant effects on glucose levels


IF has been associated with lower odds of CAD (Coronary Artery Disease) and diabetes, has been shown to reduce inflammation, enhance immune function, and have additive and possibly synergistic effects when combined with drugs.  It has been shown to enhance cancer treatment with both chemotherapy and radiation therapy and there are potential applications for IF in inflammatory disease - significantly reducing symptoms of rheumatoid arthritis and reducing inflammatory markers in asthma sufferers.


Time Restricted Fasting has been associated with reduced breast cancer risk. Positive anecdotal reports from those following the 5:2 diet include weight loss, improved asthma symptoms, increased energy, mood enhancement, reduced impact of fibromyalgia, epilepsy management, reduced blood pressure, improved fitness levels, reduction of skin irritations and improvements with glucose levels.


MORE ON THE 5:2 METHOD (The Fast Diet)

The basic concept behind The Fast Diet, the 5:2 method is  to eat normally 5 days/week and restrict dietary intake on 2 days/week to ¼ of normal level (women 500 calories (2100kJ)/day; men 600 (2500kJ). This is based on women needing 2000 calories/day and men need 2400 calories/day. You can check your BMI and BMR on the Fast Diet website.

  • Establish a realistic weight loss goal
  • Fasting days are usually non-consecutive, but this depends on individual preference.
  • Eat lean protein, vegetables and fruit on fasting days, usually as two small meals plus a few snacks.
  • A typical 500-calorie fasting day might include porridge with fresh blueberries for breakfast, a piece of fruit for a snack and a chicken and vegetable stir-fry for dinner. You can use many apps to help with counting calories.
  • Drink lots of water and calorie-free beverages such as tea, coffee (no milk or sugar), mineral or soda water with a dash of lemon or lime for flavour
  • On the 5 regular days you can eat anything, although mindful eating is still encouraged. Surprisingly, the research team that studied the diet found that people didn’t gorge themselves on off days.
  • 5:2 Fast Diet strongly discourages drinking alcohol on fasting days and suggests moderation on other days.

Upon achieving your weight loss goal, 1 day of fasting/week is recommended for maintenance.



  • Loss of body fat for overweight people is of health benefit in general
  • Research shows that people don’t tend to consume more kilojoules on the non-fasting days, or during the non-fasting period
  • Intermittent fasting appears as effective as calorie-restricted diets for weight loss
  • Fasting provides an easier weight loss plan than standard kilojoule-restricting diets – no weighing or 'forbidden' foods (a guide for fasting days is included in the Fast Diet), no restrictions during non-fasting times, limited hours/days of restriction - may all aid compliance
  • Knowing that you can indulge a little more the next day may aid compliance on fasting days on 5:2 diets
  • Fasting enables people know what hunger actually feels like, and that it’s ok to feel hungry
  • It can break the cycle of snacking
  • Research suggests that 5:2 is effective in curbing cravings
  • Some report improved sleep at night and elevated alertness during the day on fasting days and during TRF
  • For clients who won’t change (or only minimally) their dietary choices, IF can still help lower certain disease risk factors
  • Short fasting periods (1 day) enables the maintenance of muscle mass
  • As a first step alternative to pharmacological interventions to lower chronic disease risk factors, as drugs often accompanied by adverse side effects
  • No direct financial cost, and possibly even a saving on food expense



  • Intermittent fasting may be effective for some, but unsuitable for others, and some find it extremely difficult
  • Selecting a suitable fast for each individual may be a solution, eg. TRF (shorter fasting periods) rather than IF.
  • Intermittent fasting is not recommended: – during pregnancy and breastfeeding – in underweight individuals – for those with a history of eating disorders – kids, teens, frail seniors – if unwell or with a fever – in those with glucose control issues, especially T1DM. If on Warfarin it’s advisable to check with your doctor first if taking medication
  • There is limited research on long-term effectiveness or any long-term health issues related to IF
  • Traditional extended fasting can have a negative effect on female hormones, affecting menstruation and fertility. A gentler intermittent fasting approach enables women to avoid jeopardising hormones
  • Fasting diets don't necessarily encourage eating healthier foods. While maintaining a healthy body weight is important, a nutritious diet offers many more health benefits
  • Fasting may make a person irritable, faint, weak or cause headaches, and may lead to dehydration (due to the lost water component of foods). More water should be consumed and endurance activities should be avoided, on fasting days.
  • For some, fasting days may reduce physical activity.
  • Continuous extended fasting converts into starvation, where vital organs and muscles are consumed for energy. Starvation causes excessive weight loss, anaemia, chronic diarrhoea, delirium and eventually death. Intermittent therapeutic fasting should not have these adverse effects, but may still cause harm when practiced too frequently or for too many days consecutively.
  • Excessive fasting could lead to malnutrition, eating disorders or susceptibility to infectious disease



  • For weight loss, exercise on the fasting days (not endurance events), and the mornings post fast days.
  • For TRF, exercise in the morning before eating.
  • Kilojoule requirements will depend on individual BMR as per the Fast Diet website. You might need to eat more or less.
  • Eat protein, fibre and good fats for satiety, skip the refined carbs.
  • Many find breakfast the easiest meal to skip on a fast day.
  • For TRF, some prefer to start eating later to share a family meal or be sociable in the evenings.
  • Always consider the quality of the foods you’re eating - avoid processed foods
  • Different regimes may exert different effects. How much fasting is beneficial? What is the optimal frequency and duration? Stay current with the emerging research and, as always, keep in mind that every individual is different