Is intermittent fasting more effective for weight loss compared with daily kilojoule restriction?  It is a way of eating that has become more popular over the years.  While many religions have practised fasting for centuries, it is only recently that intermittent fasting has become a part of ‘dieting’ culture.  But what exactly is it?


Typically, intermittent fasting involves reducing kilojoule (energy) intake on two, non-consecutive days to around 25% of total energy needs, and then eating ‘normally’ on the remaining five days of the week.  Another version of intermittent fasting involves fasting on every alternate day and is therefore more challenging given the extra time fasting during any given week.


Followers of intermittent fasting claim that restricting kilojoules for a set number of days, is mentally more appealing than restricting kilojoules daily.  Supporters claim not only weight loss as a benefit, but improvements in cholesterol, blood pressure, and insulin resistance.  But, does intermittent fasting really result in greater weight loss compared to a standard daily kilojoule-restricted diet?


What does the evidence say?

A recent article published in the Journal of the Medical American Association (JAMA) is the first long-term randomized clinical trial conducted to date which attempts to answer this question.


The study used 100 obese adults (86 women; 14 men) who were metabolically-healthy, meaning they were obese but had no presence of metabolic diseases such as type 2 diabetes, high blood pressure or high cholesterol levels.  These adults were aged between 18-64 years of age with a mean BMI of 34kg/m2.  Participants were randomized to one of three groups, for an initial 6 month weight-loss phase, followed by a 6 month weight-maintenance phase:

  1. Alternate-day fasting – eating only 25% of energy needs on ‘fast’ days, and 125% of energy needs on ‘normal’ days
  2. Daily kilojoule restriction to 75% of energy needs every day
  3. No-intervention control


So what do the results show?  After one year, researchers concluded that weight loss in the alternate-day fasting group was not significantly different to that of the daily kilojoule restriction group.  What this means is that the amount of weight lost was similar for people in both groups at 6 months and at 12 months.  In addition, there was no significant difference between the two intervention groups at 6 months or 12 months for heart rate, fasting glucose and fasting insulin levels, insulin resistance, blood pressure, or triglycerides (type of fat found in the bloodstream).

However, results in cholesterol levels did differ somewhat.  In order to understand these results, let’s take a look at how cholesterol functions.  The body needs some cholesterol in the blood for essential functions such as producing oestrogen and testosterone, and helping the body to produce vitamin D.  In order to do this, the body produces cholesterol which is carried around in the blood by lipoproteins. Low-density lipoprotein cholesterol (LDL-C) carries cholesterol to the cells and when levels in the blood are high it can clog arteries which is why it is referred to as ‘bad’ cholesterol.  On the other hand, high-density lipoprotein cholesterol (HDL-C), also known as ‘good cholesterol’, helps to remove excess cholesterol out of cells.


So back to the study results.  When it came to cholesterol, HDL-cholesterol (‘good’ cholesterol), while significantly increased in the alternate-day fasting group at 6 months, was not different at 12 months, compared to the daily kilojoule restriction group.  More surprising was that LDL-cholesterol (‘bad’ cholesterol) was significantly higher at 12 months in the alternate-day fasting group compared to the daily kilojoule restriction group.


A rather important point to note was that the alternate-day fasting group had a higher dropout rate (13 of 34 participants) compared to the daily kilojoule restriction group (10 of 35 participants), highlighting the very real practical challenges of intermittent fasting.


Is intermittent fasting really the way to go?

Given the restrictive nature of intermittent fasting, it is not suitable for children, teenagers, highly-active people, pregnant women, those with diabetes and those with eating disorders.


It’s important to highlight that the benefits seen in this study are only seen as long as the person can maintain the diet, which in reality is unlikely.  There is little research showing the long term effects of intermittent fasting after one year, and ideally a study with little to no participant drop outs is needed.  Furthermore, it is currently unknown whether intermittent fasting increases rates of disordered eating.


While the evidence from this study shows that both intermittent fasting and a standard kilojoule-reduced diet can result in weight loss, it is important to remember that being a healthy weight is just one measure of health.  Other factors, such as the quality of a person’s diet are also important considerations that impact on health.  This is something intermittent fasting does not take into account – it focuses only on the amount of kilojoules consumed, rather than the types (quality) of kilojoules consumed.


An example to demonstrate this point, the reality is that less than seven percent of Australians currently meet their daily requirement of five serves of vegetables.  Therefore, developing healthier eating patterns and improving the quality of the diet can be far more beneficial in improving health than simply focusing on the amount of kilojoules consumed.



Take home message

The current evidence shows that intermittent fasting is not likely to produce superior weight loss, weight maintenance, or cardiovascular health protection, compared with daily kilojoule restriction diets.  In short, intermittent fasting is as effective, but not better, than a standard reduced-kilojoule diet for weight loss.  This is because, in theory, any ‘diet’ that encourages eating fewer kilojoules than expended, will result in weight loss.  However, given “diets” aren’t successful in the long run, it is unlikely intermittent fasting would be sustainable long-term.


It is more important for your health, to find an eating pattern that you actually enjoy and that satisfies you, as this is more likely to be something you will be able to continue long-term.  For some people, this may be intermittent fasting, but it is certainly not for everyone.  Because there is no one way of eating that suits everybody, please see an Accredited Practising Dietitian who can tailor and customise an eating plan suited to your lifestyle and food preferences.


Trepanowski, JF, Kroeger, CM, Barnosky, A, et al. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults. A Randomized Clinical Trial. JAMA Intern Med. 2017;177(7):930-938

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