Intermittent Fasting

Intermittent Fasting

Summer is coming and, let’s be honest, we’re all starting to think about looking our best for the beach. It’s usually a wise idea to steer clear of traditional diets, which often result in muscle and bone wastage and often do more harm than good, as well as failing as a long-term solution. Far better to change our habits as a whole, and incorporate a different “way of eating” rather than a “diet” into our lifestyles. Intermittent fasting is the hot topic in research right now and is regularly appearing in the news in some form or other. Whilst much of this research suggests increasingly positive results, with intermittent fasting demonstrated as a way of combatting inflammation, high blood pressure, unhealthy cholesterol levels and, as a way of burning fat more effectively, there are caveats to this and some more recent headlines suggested it may actually be detrimental in all of these areas (1). So is intermittent fasting the answer, or is it more complicated than that?

What is Intermittent Fasting?

Intermittent fasting, also known as time-restricted eating or cyclic fasting, simply means eating at certain times and allowing the body rest periods the rest of the time. Research usually focuses on fasting periods of between 12-18 hours and 14-16 is often enough for most people, with 18 hours only necessary if major body composition change is needed.

The most common types of intermittent fasting include:

  • Time-Restricted Feeding: As mentioned above, this is where you fast for 14-16 hours everyday and limit your eating to 8-10 hour windows. Most often, this simply involves not eating anything after dinner and skipping or eating a late breakfast the next morning. The easiest way to do this if home in time is to eat dinner no later than 6pm and aim for a 8- 10am breakfast/mid-morning meal.
  • Alternate-Day Fasting: This entails eating only every other day. On fasting days, some eat no food at all and others eat a very small amount, typically around 500 calories. On non-fasting calorie days, aim to eat normally (but healthily!)

5:2 Diet: For five days of the week, you eat normal, healthy foods as usual. For the remaining two fast days, you should restrict your caloric intake to between 500–600 calories on each of the fast days.

Health Benefits

Among its benefits, studies show that correctly executed intermittent fasting diets can increase lifespan, support healthy immune function, improve LDL particle size and triglycerides, normalize blood pressure, balance fat-regulating hormones like fat-burning adiponectin and satiety-signalling leptin so that we get hungry less, as well lower inflammation and protect the heart.

Aside from the obvious logistics that less time to eat generally equals less food going in, the ability to burn fat may be increased too. By not providing your body with a constant stream of glucose to use as its primary energy source, it will start using fat cells instead which are broken down into ketones to provide fuel. Research shows that this generally starts happening after 8-14 hours of fasting, depending on the individual doing it (2).

Much research has also suggested that intermittent fasting regulates insulin and blood glucose levels, with one study suggesting that fasting decreased blood sugar by 12% and lowered insulin levels by almost 53% (3). Amongst all this, intermittent fasting has also been shown in research to benefit brain function and protect against the damages of ageing (4).

Precautions & Caveats

If all of the above sounds too good to be true, it probably is! Most of the research has been conducted in rats, which whilst useful as a guide, do not behave metabolically in exactly the same way as humans. The few human studies there are, focus more on men than women, and there may be a very different response to intermittent fasting between the two sexes.

Whilst men and/or male rats have generally demonstrated favourable responses to intermittent fasting in research, female rats and women have not. Research suggests that rather than experience increased insulin sensitivity with fasting regimes, females may actually experience a decrease in glucose tolerance, as well as significant hormone imbalance (5). We already know that calorific restriction has proven to be detrimental for female reproductive health, resulting in a condition called hypothalamic amenorrhea, and research on fasting seems to back this up. They tend to become “masculinised” and cortisol levels are pushed up, resulting in disrupted sleep patterns, dysregulated menstruation, acne and other symptoms of hormonal imbalance. The literature on female intermittent fasting so far is sparse, but suggests it may not be ideal for women. Certainly, women of reproductive age should proceed with caution.

There are also arguments that choosing the same number of fasting hours daily stops working after a short time as the body predicts the fasting time and benefits are dulled. intermittent fasting might be best done only twice a week or month, rather than on a daily basis. For some people (particularly women), if done more frequently than this, then cortisol can spike, preventing weight loss, disrupting sleep and making the whole experience completely pointless. It’s also worth pointing out that whilst the literature suggests that overweight and obese participants of intermittent fasting appear to experience significant improvements, normal weight patients do not show the same across-the-board benefits.

Sensible Intermittent Fasting

Logically, throwing healthy eating habits to the wind and eating whatever you like during eating hours is not the most sensible approach! Don’t lose sight of what healthy eating actually means ; intermittent fasting is not a license to eat junk food the rest of the time.

Caffeine should not be consumed during fasting hours as the associated cortisol release can increase stress, drive up insulin levels and make one jittery – aim for fresh filtered water or herbal infusions.

Listen to your body and stop fasting if any unpleasant symptoms are experienced. Be especially aware of the strain on your digestion after so long without food and make the first meal of the day relatively simple and easy to digest.

Diabetics should work with their primary healthcare provider if wishing to try intermittent fasting. For people with gallstone disease, fasting may increase the risk of gallbladder problems and should also be avoided. Those with any level of hypothyroidism should also be aware that fasting can reduce T3 production.

Those who are stressed and under particular adrenal strain (i.e. sleep deprived, stressful job or personal life) should be cautious; as mentioned above, fasting can elevate cortisol levels if it goes on for too long. Aim for no more than 18 hours at any one time and break the fast gently.

Anyone with any of the above conditions might want to aim for a smaller fasting window and monitor their health with their primary healthcare provider. Aiming to eat earlier in the evenings might be the best approach, say 6-8pm, then breakfast between 8-10am, or whichever 12-16 hour window suits you best. Fasting is however NOT suitable for pregnant women or anyone with an eating disorder.

The literature in humans is sparse, especially for women, so the take home message is: listen to your body and respond accordingly! If it doesn’t feel good, then it probably isn’t.







Coriander Stone is a functional medicine-trained Nutritional Therapist with a first class degree in Nutritional Therapy. She has experience researching personalised nutrition protocols and working one-to-one with clients with a wide range of health imbalances in a clinical setting, via Skype and working as a freelance nutritional journalist. She has featured in international newspapers and had many articles published in peer-reviewed and industry-aimed magazines.  A UK native, she also speaks fluent Spanish and French and is able to offer nutrition consultations in all three languages.







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