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Intermittent fasting

*review of popular diets and research behind them

More and more of our clinic patients are trying intermittent fasting with positive feedback and results, but find it confusing to navigate via information around. Here is some information: 

What is intermittent fasting? 

Cycles of fasting periods with no food or significant restriction and “festive” periods of unrestricted eating. Intermittent fasting roots of traditional fasting, recommended as long as Socrates and all major religions. Evolution theory followers rationalize that human bodies were  formed during prolonged periods of food starvation, with an intermittent “fests”  (“mamonth”). Despite variations, all of the diets recommend at least 12 hours fasting. 

Research demonstrated that prolonged very low calorie diets can cause physiological changes that may cause the body to adapt to the calorie restriction and therefore prevent further weight loss. Intermittent fasting attempts to address this problem by cycling between a low calorie level for a brief time followed by normal eating, which may prevent these adaptations. However, research does not consistently show that intermittent fasting is superior to continuous low calorie diets for weight loss efficiency.


What are intermittent fasting regimens? 

The most common ones are:

  • Alternate-day fasting—Alternating between days of no food restriction with days that consist of one meal that provides about 25% of daily calorie needs. Example: Mon-Wed-Fri consists of fasting, while alternate days have no food restrictions.
  • Whole-day fasting—1-2 days per week of complete fasting or up to 25% of daily calorie needs, with no food restriction on the other days. Example: The 5:2 diet approach advocates no food restriction five days of the week, cycled with a 400-500 calorie diet the other two days of the week.
  • Time-restricted feeding—Following a meal plan each day with a designated time frame for fasting. Example: Meals are eaten from 8am-3pm, with fasting during the remaining hours of the day.

What research on intermittent fasting is available? 

Summary of the most interesting/exciting ones VISTA Clinic Australia would like you to know:

  1. Calorie restriction increase lifespan and improve tolerance to various stresses (in animals). All evidence in animal studies is strong, but for ethical and complience reasons, human studies evidence is still lacking.  Theory behind the intermittent fasting effect on life prolongation that the stress of fasting causes an immune response that repairs cells and produces positive metabolic changes (reduction in triglycerides, LDL cholesterol, blood pressure, weight, fat mass, blood glucose). The full research is here(health markers) and here (health effects).
  2. Interestingly, study shown that overeating of non-fasting days doesn’t “ruin” the diet effect, like it’s happening with other diet regimens. 
  3. A systematic review of 40 studies found that intermittent fasting was effective for weight loss, with a typical loss of 3-5  kg  over 10 weeks. Although significant variability in the studies, ranging in size from 4 to 334 subjects, and followed from 2 to 104 weeks. It is important to note that different study designs and methods of intermittent fasting were used, and participant characteristics differed (lean vs. obese) etc inconsistencies.  Half of the studies were controlled trials comparing the fasting group to a comparison group and/or a control group (either continuous calorie restriction or usual lifestyle), with the other half examining an intermittent fasting group alone. A brief summary of their findings:
  • Dropout rates ranged from 0-65%, which is similar to “classic” continuous calorie restriction groups. it’s  not necessarily easier to follow than other weight loss approaches.
  • Ten trials that investigated changes in appetite did not show an overall increase in appetite in the intermittent fasting groups despite significant weight loss and decreases in leptin hormone levels (a hormone that suppresses appetite).

4. A randomized controlled trial of 100 obese individuals for 1 year did not find intermittent fasting to be more effective than daily calorie restriction. Their findings when comparing the two groups (calorie restriction vs intermittent fasting):

  • No significant differences in weight loss, weight regain, or body composition (e.g., fat mass, lean mass).
  • No significant differences in blood pressure, heart rate, fasting glucose, and fasting insulin. At 12 months, although there were no differences in total cholesterol and triglycerides, the alternate-day fasting group showed significantly increased LDL cholesterol levels. The authors did not comment on a possible cause.

The dropout rate was higher in the alternate-day fasting group (38%) than in the daily calorie restriction group (29%). Interestingly, those in the fasting group actually ate less food than prescribed on non-fasting days though they ate more food than prescribed on fasting days. 

What are restrictions of intermittent fasting? 

Individuals with the following conditions should abstain from intermittent fasting:

  • Diabetes
  • Eating disorders that involve unhealthy self-restriction (anorexia or bulimia nervosa)
  • Use of medications that require food intake
  • Active growth stage, such as in adolescents
  • Pregnancy, breastfeeding

What are our practical recommendations? 

  1. Consult with your GP – they will check contraindications and arrange necessary resources. 
    Doctor also can decide to prescribe you medication to assist with initial hunger during the adjustment period. 
  2. Observe yourself – there is no similar body and no universal diet. Imagine that you are a lithium battery – assess and write down how much improvement you notice in your well beeing with different regiments. Obviously, nothing extreme. 
  3. DO not stay on this diet indefinitely. Set up a date for success assessment – when you make a decision to continue or not and it you feel better than before the diet trial.