Alternate Day Fasting: High or Low Fat Intake on Fasting Days? The Answer May Depend on Your Goals - High Fat (46%) for Fat Loss, Low Fat (23%) for Heart Health

Study suggests: Your goals may determine whether a low or high fat diet is the better base for alternate day fasting.

The beginning of a year is usually the time even SuppVersity readers begin to question their dietary regimen. For many of you it's thus also the time of the year to revise, whether new scientific evidence may indicate that what you've done so far was (a) wrong or could (b) at least be improved.

Against that background it may be worth taking a look at a bunch of recent studies; starting today with one that investigates the pros and cons of high vs. low fat dieting on an alternate fasting regimen (Varady. 2015) - pros and cons of which the study results indicate that they may depend on your goals.
Weight loss is one goal you may want to achieve by dieting is weight loss. Another, eventually more important goal is to improve your health. The latter, i.e. improving your health by lowering / improving the free fatty acid profiles via alternative day fasting was the research interest of scientists from the University of Illinois at Urbana-Champaign. In their latest experiment, Varady et al. examined how alternative day fasting (ADF) diets of different macronutrient compositions affect plasma FFA profiles in the context of weight loss, and changes in body composition and lipid profiles.

Figure 1: Changes in body composition in response to low vs. high fat alternative day fasting containing 25% or 45% of the 75% energy reduced diet on the fasting day in form of fat (Varaday. 2015).

What they found was that the low fat and high fat version of the alternate day fasting protocol in the study at hand, which contained...

• 25% of the required energy on the fasting day (day 1, 3, 5, ...), 
• 125% of the required energy on the feast days (day 2, 4, 6...) and
• had the same macro composition on both days, 

the 29 obese women (mean age ~43y) consumed for 10 weeks had similar effects on the body weight and fat of the subjects.
with a slight advantage in terms of the particularly health-relevant reductions in waist circumference in response to the low fat (ADF-LF) alternate day fasting diet, but a significant advantage in terms of total fat loss for the 45% high fat diet (ADF-HF).

Figure 2: Exact macronutrient composition in grams for someone consuming 2000kcal per day;  in % that's 45/15/40% fat, protein carbohydrate for the high fat and 25/15/60% for the low fat group (Varaday. 2015 as in Klempel. 2014)

Now, body fat is only one of the factors that will have significant effects on your health, the levels of glucose, triglycerides and cholesterol constitute the 2nd piece to the "health puzzle".
And here the low fat alternate day fasting diet had significant advantages.

Figure 3: Changes in total cholesterol LDL, triglycerides, HDL (no change!) and glucose (Varaday. 2015).

In view of the fact that the same goes for "almost all FFAs in the ADF-LF group decreased whereas changes were only noted in LA and LNA in the ADF-HF group" - changes that correlated directly with the reduction in waist circumference (see Figure 4, right).

Figure 4: Correlation between decreases in waist and the levels of ALA (LNA; n3), linolic acid (LA, n6), palmitic acid (PA, SFA) and oleic acid (OA) in the ADF-HF group, similar correlations were not observed in the low fat group, where the FFA levels dropped irrespective of changes in weight circumference, left; mean free fatty acid levels before and after the 10 week intervention in the low fat (ADF-LF) and high fat (ADF-HF) group, right (Varaday. 2015).

In view of the fact that elevated total and individual plasma FFA concentrations observed in obesity have been linked with cardiovascular disease risk. More specifically, high levels of fatty acids ...

• Learn more about alternate day fasting in general in a previous SuppVersity article.

  predict sudden cardiac death in a 6.85-year follow-up of 3315 patients after coronary angiography; even after adjusting for all other CVD risk factors having elevated FFA levels was still associated with a 76% increased risk of sudden cardiac death (Pilz. 2007),
• impair glucose uptake and will thus increase the risk of developing type II diabetes, which in turn is one of the major risk factors for developing the metabolic (Boden. 1994),
• especially high levels of palmitic acid (saturated fatty acid) are associated with increased risk of triglyceridemia and abdominal obesity which in turn are linked to cardiovascular disease risk (Paillard. 2008).

Accordingly, the authors are right when they say that the fact that the low fat variety of the alternative day fasting diet may due to being "more effective at lowering FFA" could be a tad bit more effective when it comes to its cardio-protective effects. They do yet also point out that "[f]uture studies might include individual FFA profiles when evaluating macronutrient composition, as the effects of specific FFAs in this context are not well known" (Varaday. 2015).

Thus the effects of e.g. higher omega-3 intakes (in the study at hand total PUFA was 25g and 12g in the high fat and low fat group), as well as the effects of higher protein intakes, specifically on the fasting days, where someone with a baseline intake of 2,000kcal would consume only 18.75g protein and thus way too little for optimal lean mass retention are in fact parameters that would have to be studied in future studies.
References:

• Boden, Guenther, et al. "Mechanisms of fatty acid-induced inhibition of glucose uptake." Journal of Clinical Investigation 93.6 (1994): 2438. 
• Fearon, Kenneth, et al. "Definition and classification of cancer cachexia: an international consensus." The lancet oncology 12.5 (2011): 489-495.
• Heilbronn, Leonie K., et al. "Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism."The American journal of clinical nutrition 81.1 (2005): 69-73.
• Klempel, Monica C., Cynthia M. Kroeger, and Krista A. Varady. "Alternate day fasting (ADF) with a high-fat diet produces similar weight loss and cardio-protection as ADF with a low-fat diet."Metabolism 62.1 (2013): 137-143.  
• Paillard, François, et al. "Plasma palmitoleic acid, a product of stearoyl-coA desaturase activity, is an independent marker of triglyceridemia and abdominal adiposity." Nutrition, Metabolism and Cardiovascular Diseases 18.6 (2008): 436-440.
• Pilz, Stefan, et al. "Elevated plasma free fatty acids predict sudden cardiac death: a 6.85-year follow-up of 3315 patients after coronary angiography." European heart journal 28.22 (2007): 2763-2769.
• Varady, Krista A., et al. "Modified alternate-day fasting regimens reduce cell proliferation rates to a similar extent as daily calorie restriction in mice." The FASEB Journal 22.6 (2008): 2090-2096.
• Varady, Krista A., et al. "Effects of weight loss via high fat vs. low fat alternate day fasting diets on free fatty acid profiles." Scientific Reports 5 (2015).