Intermittent Fasting - Fact or Fad Series.

Intermittent fasting (IF) is a diet strategy involving alternating periods of eating and extended fasting (meaning no food at all or very low calorie consumption).  

Can this method be better for weight management/weight loss and health versus conventional energy restricted diets (CERD)? 

Image 1. Intermittent Fasting - An Umbrella Term

Confusingly, IF is a quite large umbrella term of different fasting methods. All methods involve some form of time restrictive feeding, but allow one to eat freely within the feeding hours. Some of the main fasting techniques include: 

• 8:16 Method (One Of The Most Popularised Form)

• Warrior Method

• Alternative Day Fast

•  5:2 (Fast Diet) (See Image 1)

Both fasting  and conventional weight restriction can result in reduced energy intake, and potential weight loss. What makes fasting different from CERD is it’s unique “re-feed” period which follows the fast. This re-feed is important as it may provide qualities responsible for adaptions in weight loss, that conventional reduced calories diets do not. 

 What are the benefits? 

• Body mass: Research supports that IF methods can support weight loss (when adhered to – like so many diets), however much debate remains whether this method has more positive outcomes then CERD (4;5).Lean mass is important to overall health (1), and for many people looking and feeling good. Muscle mass can potentially be negatively influenced if unfed (insufficient protein). However it seems that once adequate protein and energy intake is consumed in feeding window, in addition to resistance training, that risk lean mass loss can be avoided (7). Knowing the appropriate intakes is key in fasting. 

•  Easy to follow (If it suits you): For fasting, the rules are simple, eat in X hours, don’t eat in Y hours. There are some important considerations to dietary prescription for protein, exercise timing and what you can and can’t have in fasted period (see image 1), but overall no huge learning involved. In addition there is no counting, or apps are required, so even more user friendly. 

Why it may work! 

• Re-feeding: The unique part of IF and where it may differ is the re-feed nature. Energy restriction can result in changes in key modulators that influences metabolic regulation – (i.e. during calorie restriction our bodies adapt to less energy provision, meaning bodies require less calories for a given function). This means that our bodies do not require as many calories for its basic functioning. So this adaption in the body can actually work against weight loss. One hypothesis is that the nature of refeeding potentially prevents these opposing changes in metabolism, thus potentially aid weight loss (4). However, research still is not conclusive to whether a re-feed, that is not overfeeding (excess calories over needs), can have this effect. 

•  Restriction of calories:Simply, less time allowance to eat calories, permits for less calories consumed, resulting in lower energy intake and potential weight loss. 

•  Behaviour:Our poor habits strongly dictate health, in this case weight management. If a poor habit is prevented through the nature of restrictive feeding time, it may benefit your goal . For example, many people struggle with late evening snacking. If you cannot eat after 8pm, you start to remove this habit which may to the reason for your weight issues. 

So what if I want to try this – it sounds like it would suit my lifestyle (see image 2) .

Image 2 :Example of what an 8 hour feeding window and a 16 hour fast may look like.

This is a sample of an 8 hour fast. A person’s lifestyle will dictate fasting hours, however keeping your feeding window in day light hours seems logical due to the effects food intakes can have on circadian rhythm (body clock), which can impact health (2).

As you can see protein is important in the meals to potentially prevent lean mass loss risk. Within your feeding period you want to ensure you hit protein targets. Training session is put into non fasting hours, this is be ensure energy and recovery can be optimised (4). Exercise, particularly resistance training,  may be hugely beneficial in health and attenuating lean mass. Water and black coffee (no sugar) are permittable throughout fasting hours.

 This diet IS NOT for some people, For example:

• Individuals with a history of eating disorder/disordered eating: This group should steer clear as fasting increases risk of eating disorder patterns (6).

•  High level training:  Energy restriction with high levels of training (e.g. athlete), may result in a loss in lean mass (4), this could be more negative to performance than positive. Research suggests that leaner individuals are at an increased risk of losing fat free mass versus obese/overweight individuals (3).

Image 3. Fasting and feeding window permitted food and beverages.

Limited research:It needs to be noted that much of the research to date has been carried out on animal models (rats), therefore it cannot be directly said that these findings can be replicated in humans. 

There does appear to be potential in IF, however more research is required due to different fasting methods, populations etc., to determine whether IF could be better for weight management over conventional methods.   Additionally, it should be noted that there is high dropout rate throughout research (4), possibly due to the nature of the diet. This suggest it may not be for a lot of people. 

Concluding thoughts: Almost any good eating pattern and exercise program can help a person reach goals and feel better, when adhered to. IF may have some benefit to individuals for weight maintenance and health. To date, research fails to strongly support that its use for weight loss is bigger/better when compared to conventional calorie restriction. Moreover, some evidence suggests it may aid hampering of the metabolic actions that occur during weight loss.  However, this diet is not suited to everyone - high dropout is apparent in research, suggesting it may be hard to stick to.  Intermittent fasting is not recommended for those who have/previously suffered from disordered eating, or suffer from medical conditions. On the other hand it may play advantages to creating better mindfulness around food habits, appetite control and is simple enough to follow from a knowledge point of view. 

Take Home: It appears that it is a method that can work. Your lifestyle, personal preferences, personality type, goals and determination would dictate whether it suits you. However, adopting a healthier, regular eating patterns may be a better place to start. If considering it, you should look for assistance from a qualified professional. Overall, just like other diets, Intermittent fasting is another tool that may benefit a person, however, needs to be followed correctly. 

VERDICT : Potential FACT (for the right person).

References 

1.    Deer, R. R., & Volpi, E. (2015). Protein intake and muscle function in older adults. Current opinion in clinical nutrition and metabolic care, 18(3), 248.

2.    Güldür, T., & Otlu, H. G. (2017). Circadian rhythm in mammals: time to eat & time to sleep. Biological Rhythm Research, 48(2), 243-261.

3.    Heymsfield, S. B., Gonzalez, M. C., Shen, W., Redman, L., & Thomas, D. (2014). Weight loss composition is one‐fourth fat‐free mass: a critical review and critique of this widely cited rule. Obesity Reviews, 15(4), 310-321.

4.    Peos, J. J., Norton, L. E., Helms, E. R., Galpin, A. J., & Fournier, P. (2019). Intermittent dieting: theoretical considerations for the athlete. Sports, 7(1), 22.

5.    Seimon, R. V., Roekenes, J. A., Zibellini, J., Zhu, B., Gibson, A. A., Hills, A. P., ... & Sainsbury, A. (2015). Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Molecular and cellular endocrinology, 418, 153-172.

6.    Stice, E., Johnson, S., & Turgon, R. (2019). Eating Disorder Prevention. Psychiatric Clinics, 42(2), 309-318.

7.    Tinsley, G. M., Forsse, J. S., Butler, N. K., Paoli, A., Bane, A. A., La Bounty, P. M., ... & Grandjean, P. W. (2017). Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European journal of sport science, 17(2), 200-207.