Article by Lisa Sayers

With many of us having gained unwanted pounds over the festive season (easily done!) we may now be looking for the most ‘painless’ way of getting rid of it. Could intermittent fasting be the answer? Intermittent fasting (IF) involves a fairly radical approach to weight loss. It is not so much a diet, but an eating pattern where you make a conscious decision to skip certain meals. By fasting and then feasting on purpose, IF involves eating your calories during a specific window of the day, and choosing not to eat food during the rest. Depending on who you listen too IF may involve a fast for 24 hours, fasting for part of the day two days a week, fasting on alternative days, or even over five consecutive days every two months to achieve sustained weight loss.

I would suggest that fasting for more than two days per week may lead to nutrient deficiencies if you are not consuming an optimal diet. Prior to commencing any radical change of diet you should always consult your G.P and consult a qualified dietician or nutritional therapy to ensure that you are eating optimally.

According to the media IF appears a fast, effective way to lose weight, promote health, and doesn’t involve the drudge of daily deprivation which you may experience on the continuous calorie restriction of a regular diet! Many of you may have heard of IF and have wondered whether this might be the way forwards for you.

So, does IF really work?

Clinical trials have generally shown significant weight loss (particularly from fat and not lean muscle mass). Unfortunately research into health claims is based on small scale human and animal studies. The basis behind IF is sound as it is based on reduced calorie intake, and the possibility that our bodies are designed for periods of fast as our ancestors were designed to be ‘hunter gatherers’ whom didn’t have a constant food supply.

 How does IF work and is it just a calories-in calories-out equation?

When you eat a meal, your body processes that food and absorbs it into your blood stream. Your body will choose to use this readily accessible energy in your blood stream, rather than the fat you have stored.

During the “fasted state”, your body doesn’t have a recently consumed meal to use as energy, so it is more likely to pull from the fat stored in your body, rather than the glucose in your blood stream or glycogen (stored sugar) in your muscles/liver. The same goes for exercising in a ‘fasted’ state.  Without a ready supply of glucose and glycogen to pull from (which has been depleted over the course of your fasted state), your body is forced to adapt and pull from the next most available source of energy available to it: the fat stored in your cells.

Our bodies react to energy consumption (eating food) with insulin production (insulin is a hormone that makes food available to cells in the body).  Essentially, the more sensitive your body is to insulin, the more likely you’ll be to use the food you consume efficiently, which can help lead to weight loss. Body cells are more sensitive to insulin following a period of fasting. Compare this to a regular day (no IF).  With insulin sensitivity at normal levels, any food consumed will see full glycogen stores, enough glucose in the blood stream, and thus be more likely to store any food intake ‘surplus to requirements’ as fat.

Also your growth hormone is increased during fasted states (both during sleep and after a period of fasting) and combined with increased insulin sensitivity you’re essentially priming your body for muscle growth and fat loss.

What are the other health benefits of IF?

Research suggests that IF may have other benefits other than fat loss such as:

Reduced:

  • Markers of inflammation (including CRP, IL-6, TNF, BDNF, and more)
  • Oxidative (cellular) stress (using markers of protein, lipid, and DNA damage)
  • Risk of cancer particularly breast and prostate
  • LDL (‘bad cholesterol’), and triglyceride levels.
  • Damage to brain cells and risk of Alzheimer’s disease.

Increased/Improved:

  • Increased human growth hormone which helps increase lean muscle mass
  • Improved cellular turnover and repair
  • Increased production of the hormones leptin and ghrelin which are responsible for hunger signals and signals that you are full
  • Increased fat burning during the fast
  • Production of the hormone adinopectin which research suggests improves life longevity
  • Improved brain health/function and response to stress
  • Increased metabolic rate later in the fast (stimulated by epinephrine and norepinephrine release)
  • Appetite control (perhaps through changes in  the hormones leptin, PPY and ghrelin)
  • Blood sugar control (by lowering blood glucose and increasing insulin’s action)
  • Cardiovascular function (by offering protection to the blood vessels to the heart)
  • Effectiveness of chemotherapy (by allowing for higher doses more frequently)

Which intermittent fasting diet works best?

We have recently been bombarded with a variety of IF diets. There is the 5:2 diet where on two days of the week women restrict calories to 500 calories and men to 600 calories, and the other 5 days eat normally. More recently, there is the 4:3 diet whereby you calorie restrict in the same manner for 3 days instead of two. Obviously the more days you fast the greater the caloric restriction (and possibly the greater the feeling of deprivation which may affect compliance), and the greater the weight loss. However research suggests that when fasting is more frequent a contribution of the weight loss is from lean muscle mass which is undesirable.

Does the fasting need to involve such a severe calorie restriction?

Generally intermittent fast suggest a reduction of 75% of your daily calorie intake on fast day which amounts to the 500 calories for women and 600 for men. Results from IF research in humans has been studied with the above calorie intake. This does not mean that IF wouldn’t work with a slightly more generous amount of calories, and some studies show a similar impact on weight loss and health benefits that are associated with IF. Personally I would go for the minimum amount of change with the maximum results. This may mean trying different versions of IF and monitoring results (with scales, a tape measure, quality body composition scales etc.) to see which works best for you.

Does it matter when you eat your calories on your fast days?

Most research results are based on subjects fasting for 16-18 hours on fast days e.g. from 8pm to 12pm on the following day, with calories consumed in the remaining 4-6 hour time window. I would suggest that the fast be started after an evening meal which seems to lead to fewer problems with disrupted sleep. The idea of fasting for such a long period may put you off and may be uncomfortable at the outset, as our bodies get into a habit of anticipating foods at certain times in the day which is accompanied by an increase in hunger hormones and digestive enzymes. Try persisting with IF for a two week trial to allow your body a chance to adapt ‘hormonally’ to a new routine.

Can I do IF I participate in a regular exercise schedule?

Yes, you can. Glycogen (the sugar stored in your muscles and liver that your body burns as fuel when necessary) is depleted during sleep (fasting), and will be depleted even further during exercise, this may further increase insulin sensitivity. Food consumed immediately following a workout will be stored most efficiently: mostly as glycogen for muscle stores, burned as energy immediately to help with the recovery process, and with minimal amounts stored as fat.

For example you can work out in a fasted state then consume half your calories for the day after you exercise and consume the rest of your calories later that day. I would suggest though that you choose to perform more intense exercise on non-fasting days. If you perform exercise on a regular basis it would be wise to consult a dietician or nutritionist to sort out a nutrition plan. This will ensure that your diet is optimal to help you cope with the increased demands imposed on your body from regular exercise.

“Where will I get my energy for my workouts?  Won’t I be exhausted and not be able to complete my workouts if fasting?” 

This was also a concern of mine, but your body can function and even thrive despite not eating a pre-workout meal.

In fact fasted training may result in better metabolic adaptations (which may improve performance) and improved muscle protein production.

 “Won’t fasting cause muscle loss?”  

This is another unfounded concern. Research suggests that our bodies are very adept at preserving muscle even when fasting and protein can be consumed and absorbed within a limited time window and have no impact on body composition.

Is IF suitable for everyone?

IF may not be suited to everyone and I strongly recommend that you consult with your GP if you are pregnant or suffer with or have a history of:

  • Diabetes
  • Blood sugar dysregulation
  • Eating disorders
  • Chronic stress

Possible side effects (these are usually short lived until our body adapts to a new eating routine) are listed below:

  • Irritability
  • Anxiety
  • Interrupted sleep
  • Less energy on fasting days
  • Bad breath
  • Feeling cold on fasting days
  • Headaches on fasting days

Other concerns?

“Will IF lead to reduced energy, focus, and extreme/unpleasant hunger and misery during the fasting period?”

This was the biggest concern of mine (and it seems others). Research suggests that it takes approximately 84 hours of fasting to affect blood sugar levels so a 16-24 hour fast period shouldn’t affect us. Once you have gone through the initial adaptation stage you will function well on your fasting days as your appetite hormone ghrelin production will become reduced.

“What about my body going into starvation mode from not eating and reducing my metabolic rate (the rate at which I burn calories)?” 

Now, the thought process here is that when we fast our body assumes calories aren’t available, and thus chooses to store more calories than burning them; therefore eliminating the benefits of weight loss with fasting. Fortunately, this is NOT true.

As Martin Berkhan (nutrition consultant)says the earliest evidence for lowered metabolic rate in response to fasting occurred after 60 hours (-8% in resting metabolic rate). Other studies show metabolic rate is not impacted until 72-96 hours have passed. Seemingly paradoxical, metabolic rate is actually increased in short-term fasting…Studies have shown an increase of 3.6% – 10% after 36-48 hours. The hormones adrenaline/noradrenaline sharpens the mind and makes us want to move around, encouraging us to seek for food, or for the hunter to kill his prey, increasing survival.”

Dangers:

  • Unhealthy food behaviours/obsession with food
  • Overeating or unhealthy eating on non-fast days

Possible Food Plan

If you are restricting your calories it makes sense to choose quality, fresh, unprocessed, nutrient dense foods which are high in protein, vegetables and fibre which will help satisfy hunger. Personally I would also opt for quality foods on non-fast days to further benefit your health.

An example fast day food plan would be as follows:

Skip breakfast

Lunch 12pm- Portion of homemade chicken and spring vegetable soup (approx. 200 calories).

Evening meal-75g poached salmon fillet served with stir fry vegetables (broccoli, onions, peppers, courgettes, baby corn etc. dressed with lemon juice and ginger (approx. 300 calories). 100g blueberries (70 calories), 2 tablespoons of non-fat Greek yoghurt (approx.30 calories).

 

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