8 Wks W/ Weekly Fasting Day Trigger 6% Reduction of Body Fat % + Improved Mood on Follow Up | Plus: The Three Main Mechanisms Behind Intermittent Fasting's Health Benefits

On fasting days <300ml of vegetable broth, juices or teas were OK.

Since the title of the study already gives it away, I suggest that we address the phrase "non-randomized", which describes an essential characteristic of a recent 8-week study that was conducted by scientists from the Freie Universität Berlin (Germany), right away. Yes, the study was designed as a non-randomized controlled clinical trial with two arms, involving healthy volunteers only. And yes, it is indeed very likely that the subjects who chose to be in the fasting group had a positive bias towards 'not eating' once a week...

...but hey, let's be honest: Isn't that the "real world"? I mean people who will subscribe to any form of intermittent fasting protocol usually do so voluntarily. The fact that the study was nonrandomized is thus in line with the authors' intention which was to "evaluate whether intermittent fasting is an effective preventive measure and whether it is feasible for healthy volunteers under everyday-conditions." (my emphasis in a quote from Kessler 2017).
The study itself consisted of an 8-week intervention period, followed by a four-month follow-up (the total study duration was thus 6 months). Outcomes were assessed at baseline, after eight weeks, and after six months. As previously hinted at, fasting was not obligatory, volunteers who were not interested in fasting served as a control group.

The intervention itself is easy to describe: Participants in the fasting group were asked to continue their regular nutritional habits on the non-fasting days, while the control group maintained their habitual nutrition throughout the whole period. More specifically, ...

• fasting was done on a self-chosen weekday (e.g. Monday) 
• patient adherence was defined by conducting at least six of the eight eight overall days of fasting during the eight week intervention period
• fasting days were defined as days during which the subjects abstained from solid food for at least the period between 00:00 and 23:59, and accumulated a maximum total energy intake of 300 kcal/d resulting from defined fasting beverages
• allowable "fasting beverages" were standard fruit and/or vegetable juices 2 x 200 ml/d, clear vegetable broth (maximum 300 ml/d), ≥ 750 ml/d hot, unsweetened herbal teas, ≥ 1500 ml/d of non-sparkling, resp. tap water at room temperature
• for better compliance cardamom, vanilla, and cinnamon were allowed in small quantities in order to enhance the taste of grain based liquids
• unsweetened black tea, green tea, and black coffee were also allowed in small quantities (maximum 2 servings)

A sample fasting day: 200ml fruit or vegetable juice in the morning, 300ml vegetable stock for lunch, 200ml vegetable or fruit juice in the evening plus 2250 ml of tea and water distributed over the whole day. Laxative measures before, during and after the fasting days were not part of the protocol (e.g. standard Polyethylenglycol solution, Glauber or Epsom salt).

The analysis of the subjects' (N=22 in the fasting, N=14 in the control group) baseline data showed no significant between-group differences. Overall, the scientists observed that the "[b]aseline values for participants of both groups reflect a very healthy, middle-aged and predominantly female population" (Kesseler 2017) - a group with a high variance in BMI (despite normal baseline BMI, hip measurement and abdominal girth values) and a similar distribution pattern for IGF-1 baseline values.

Adherence to fasting was OK - accordingly, it doesn't mess with the results

Of the twenty subjects in the intervention group, nine subjects completed six fasting cycles, four subjects completed seven fasting cycles, and seven subjects completed eight fasting cycles.

Figure 1: From baseline, to wk 8 there was a sign. reduction in body fat % (relative 6%, absolute -1.79% | Kressler 2017)

In view of the fact that the scientists' sensitivity analysis that included only patients with eight cycles revealed no significant differences for the evaluated outcomes, it doesn't seem as if the failure to adhere to all 8 fasting days in 50% would have ruined the data, though.

The number of adverse events, i.e. 69 vs. 17 in the fasting vs. control group confirms that fasting, especially when your body isn't accustomed to it, can have side effects.

The most common side effects that could be related to fasting were headache, migraine, nausea, ravenousness, circulatory disturbance, hunger, general feeling of weakness, tiredness, stomach ache, meteorism, heartburn and cold sensations in the body.

The beneficial effects of fasting on (a) total body fat and (b) mood and anxiety scores were small, but measurable and statistically significant... albeit probably without practical relevance. 

For me, personally, it is not surprising that an intervention that consisted of only one fasting day per week did not have statistically significant effects on the subjects' body weight, BMI, glucose management or blood pressure. In fact, I am rather surprised that Kessler et al. found significant treatment effects on total body fat and the results of the HADS mood and anxiety test.

Figure 2: Changes in HADS scores and blood pressure from baseline to wk 8 (V1) and 6-mo follow-up (V2 | Kessler 2017)

Even if you're a fasting advocate, though, you will probably have to agree with the scientists and admit that "none of the between-group differences were clinically relevant" (Kessler 2017).

The assumption that the mood changes, the authors detected after the follow-up were a result of fasting seems to be very questionable, ... to say the least.

This is particularly true in view of the fact that the pronounced improvement in HADS scores occurred after the intervention phase. At the end of the 8-week intervention, the changes in HADS total scores were identical in both groups (-0.82±2.67 for fasting, -1.93±3.34 for control, p = 0.39). The subsequent increase which was supposedly related to the previous fasting could thus have been mere coincidence - or, even worse, a result of the subjects being allowed to finally eat whenever you wanted, again ;-)

Similar caution should be exerted with respect to the - on an absolute basis - quantitatively small changes in body fat.

While the reduction in body fat occurred, when you would expect to see it, the absolute changes were small (from 28% to 26%) and despite their statistical significance, potentially an artifact of the measuring method. Especially in view of the fact that similarly relevant changes in waist circumference were not observed, it is furthermore questionable, whether that's metabolically relevant visceral and belly fat or rather relatively benign appendicular fat the subjects lost.
References:

• Conley, Marguerite, et al. "Is two days of intermittent energy restriction per week a feasible weight loss approach in obese males? A randomised pilot study." Nutrition & Dietetics (2017).
• Kessler, Christian S., et al. "A Non-Randomized Controlled Clinical Pilot Trial on 8 Weeks of Intermittent Fasting (24h per week)." Nutrition (2017).
• Patterson, Ruth E., and Dorothy D. Sears. "Metabolic Effects of Intermittent Fasting." Annual Review of Nutrition 37.1 (2017).