Ever missed a meal? Chances are that you have. Now if you add a little bit of structure to the meal skipping, say miss breakfast so that the time between dinner and the next meal is around 16 hours, then based on the newly popular intermittent fasting diet you may be onto something. Or …. is it just another fad diet?
What is intermittent fasting? #
Fasting is not a new concept. For centuries, people have temporarily restricted their food intake as a means a way of life (our hunter gatherer ancestors) and for religious reasons. Devotees of fasting have long claimed it brings physical and spiritual renewal.
In the past few years, different intermittent fasting methods have gained popularity. Intermittent fasting is the process of cycling in and out of periods eating and not eating. The different methods are:
- Alternative-day fasting: This method requires you to restrict all food for 24 hours, once or twice a week.
- Whole-day fasting: Commonly also known as 5:2. This approach to fasting advocates no food restriction five days a week, cycled with a 500 — 600 calorie diet the other two days of the week.
- Time restricted feeding: Typically, with this one, eat all your daily calories within a shortened period (typically 6 ‑8 hours) and fast for the remaining 14 – 16 hours. You can do every day, or a few times week.
The research so far… #
The thing to point out early on is that the research on IF is mainly in animal studies and although there are a few human studies available they are relatively short-term studies.
The studies on animals show strong evidence that calorie restriction has been shown in animals to increase lifespan and improve various metabolic processes which in turn have a positive effect on many inflammatory pathways. They also show that fasting has a positive impact on anti-ageing and overall longevity.
One of the primary mechanisms that makes intermittent fasting so beneficial for health is related to its impact on your insulin sensitivity. High levels on insulin over time promote inflammation and fat storage in the addition, hunger is less likely to be experienced as we never really let ourselves get hungry and as a result fat is more likely to be stored in the liver. The act of fasting is believed to cause an immune response that repairs cells and regulates insulin control. Research also shows fasting decreases the accumulation of oxidative radicals in the cell, and thereby prevents oxidative damage to cellular proteins, lipids, and nucleic acids associated with aging and disease.
The research on human studies have produced conflicting evidence. For example, a recent review (40 studies) of the literature looked at the impact of fasting on weight loss. They found that intermittent fasting when done correctly (hold on to the word correctly its important!), was effective for weight loss. Interestingly, there were no significant differences in blood pressure, heart rate, fasting glucose and fasting insulin with the subjects following IF and those following other general healthy weight loss regimes. The results also suggested that it was unclear if intermittent fasting was superior to other weight loss methods in regard to decreased appetite and compliance rates. The different modes of fasting as well as the mix of participant characteristics (lean vs. obese) is worth taking note when interpreting these results.
More high-quality studies including randomised control trials (the gold standard in research) with a follow-up of greater than one year are needed to show a direct effect and for us to clearly understand who benefits the most from IF and how it should be done for each population group.
One size doesn’t fit all. #
If you already have a stable and healthy eating pattern (you consistently eat in balance and enough) and you would like to lose weight or optimise your insulin sensitivity then IF could be something you try as you could repeat the benefits. On the contrary, if you are already a bit of a faddy and erratic eater then the risk of IF becoming a faddy diet is very high. Time and time again, within my clinical practice, it is common to see people following a feast and famine IF pattern of eating which does more harm than good! There is no point fasting one day and then feasting the next day – it just won’t do you any favours! Similarly, more is not better. Even with fasting — moderation is key. It’s not about trying to do as many fast days as possible either. This is called disordered eating.
Infact, people with a history of eating disorders, or those using medications that require food intake (type 1 diabetics), those still actively growing (teenagers), pregnant or breast-feeding women should not be fasting intermittently.
So what does this mean for us? #
There is more evidence building up to show that, for some population groups, there are many benefits to IF, however more research is needed for us to fully understand the therapeutic benefits. Within my own clinical practice, many of my clients who follow an IF pattern of eating correctly repeat the benefits in terms of weight loss and metabolic benefits. In addition, many clients find that IF is a good tool that helps many to get in tune with their hunger and fullness signals. If you want to dabble in IF, my advice is that you speak to a dietitian or a registered nutritionist so that they are able to recommend a method of fasting that works specifically for you.
References
- Patterson et al. 2017. Metabolic Effects of Intermittent Fasting. Annu Rev Nutr. 21;37:371 – 39
- Tinsley et al. 2015. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015 Oct;73(10):661 – 74.
- Horne et al. 2015. Health effects of intermittent fasting: hormesis or harm? A systematic review. Am J Clin Nutr. 2015 Aug;102(2):464 – 70
- Ganesan K et al. 2018. Intermittent Fasting: The Choice for a Healthier Lifestyle. Cureus. 2018 Jul 9;10(7):e2947
- Mattson M et al. 2017. Impact of intermittent fasting on health and disease processes. Ageing Res Rev, 39: 46 — 58
