Energy Metabolism and Intermittent Fasting: The Ramadan Perspective

Abstract

Intermittent fasting (IF) has been gaining popularity as a means of losing weight. The Ramadan fast (RF) is a form of IF practiced by millions of adult Muslims globally for a whole lunar month every year. It entails a major shift from normal eating patterns to exclusive nocturnal eating. RF is a state of intermittent liver glycogen depletion and repletion. The earlier (morning) part of the fasting day is marked by dominance of carbohydrate as the main fuel, but lipid becomes more important towards the afternoon and as the time for breaking the fast at sunset (iftar) gets closer. The practice of observing Ramadan fasting is accompanied by changes in sleeping and activity patterns, as well as circadian rhythms of hormones including cortisol, insulin, leptin, ghrelin, growth hormone, prolactin, sex hormones, and adiponectin. Few studies have investigated energy expenditure in the context of RF including resting metabolic rate (RMR) and total energy expenditure (TEE) and found no significant changes with RF. Changes in activity and sleeping patterns however do occur and are different from non-Ramadan days. Weight changes in the context of Ramadan fast are variable and typically modest with wise inter-individual variation. As well as its direct relevance to many religious observers, understanding intermittent fasting may have implications on weight loss strategies with even broader potential implications. This review examines current knowledge on different aspects of energy balance in RF, as a common model to learn from and also map out strategies for healthier outcomes in such settings.

Keywords: Fast; Ramadan; energy expenditure; intermittent; weight.

Figure 1

Time-dependent Changes in Weight during Prolonged Fasting (31 Days). Adapted from: Francis Gano Benedict: A study of Prolonged Fasting. (a), Daily Net Weight Loss: calculation of daily weight reduction in 31 days (D) of fasting. Initial weight was 59.86 kg at D1, final weight was 47.47 kg at D31, total weight loss −12.4kg. R² = 9798 indicated a linear relationship between time and net weight loss. (b) Changes in Rate of Daily Weight Loss: relative to starting rate of weight loss, rate of weight loss per day indicates various changes whereby a steep rate of weight loss we observed in the first five days of fasting (D1–5; Maximum Rate 0.67), followed by a slower rate of weight loss in the following 10 days (D5–15; Maximum Rate 0.64), which decreased further in the next 10 days (D15–25; Maximum Rate 0.47) before reaching a plateau in the last five days of the fasting month (D25–30; Maximum Rate 0.42).

Figure 2

Changes in Feeding Patterns and Energy Intake during Various Fasting Periods. The five feeding and fasting patterns are: (I) normal feeding, (II), calorie restriction, (III) intermittent fasting (e.g., 5:2), (IV) Ramadan fast and (V) prolonged fasting and starvation. (a) Hourly Differences in Feeding Patterns between Various Fasting Models: hourly timings of feeding and energy intake (meals) are indicated per day in relation to fasting periods (arrows) and reflected in glycaemic control (traces). (b), Daily and Weekly Differences in Feeding Patterns Between Various Fasting Models: daily and weekly feeding patterns are mapped against calorie intake which can be regular such as in in normal feeding (I), indicated by single colour arrows or a combination of low, normal or high calorie intake as in intermittent fasting (III), indicated by mixed colour arrows. Ramadan fast (IV) is unique as it combined low and high calorie intake as indicated by the two single colour arrows. The first week is broken down into seven individual days. Weekly indications follow thereafter.

Figure 3

Energy intake (EI) recommendations and resultant weight changes in Ramadan and non-Ramadan periods. Energy intake recommended guidelines for female and male adults. (a) indicates values for the (1) UK 2250 kcal/day (female 2000 and male 2500 kcal/day), (2) the USA 2300 kcal/day (female 2000 and male 2600 kcal/day) and (3) for Australia 2225 kcal/day (female 2010 and male 2600 kcal/day). Collectively, an average adult consumes ~2270 kcal/day (female 2003 and male 2533 kcal/day). (b), Energy intake recommendations during Ramadan in comparison to standard and low calorie diets. in order of left to right: based on the calculated average of 2270 kcal/day as a standard adult EI (Figure 3A), a healthy Ramadan diet matched calorie intake is achievable. In reality, a higher EI is experienced in Ramadan (~3000 calories). However, weight maintenance (at 1800 kcals/day) is achievable during Ramadan as suggested by Diabetes and Ramadan (DaR) Alliance Ramadan Nutrition Plans (RNP) recommendations. This holds true for weight loss at the 1500 and 1200 kcals/day calorie EI for both non-Ramadan and Ramadan periods.

Figure 4

Energy expenditure and physical activity pre-, during and post-Ramadan. (a) Box plot of daily total number of steps during and post-Ramadan. The effect of Ramadan fasting on activity in 11 participants. (b) Box plot of total number of steps at different periods within one day (per night, morning, afternoon, and evening) during and post-Ramadan in 11 participants. Comparisons made with the Wilcoxon signed-rank test. Total mean ± SD number of steps per day (9950 ± 1152 compared with 11,353 ± 2053, p = 0.001), activity in the morning (1974 ± 583 compared with 3606 ± 715, p = 0.001) and afternoon (3193 ± 783 compared with 4164 ± 670, p = 0.002) were significantly lower during Ramadan compared with post-Ramadan. Nocturnal activity was higher during Ramadan (1261 ± 629 compared with 416 ± 279, p = 0.001). No significant difference in evening activity levels between during and post-Ramadan periods was observed. (c) TEE and RMR during and post-Ramadan: the correlation between TEE and weight during and post-Ramadan in 10 participants. No significant difference between Ramadan and post-Ramadan regression lines (ANCOVA; t = 0.35, p = 0.727); the main factor influencing TEE was body weight (t = 2.72, p = 0.015).