FASTING is not a new diet fad: the effects of three main regimes have been researched scientifically.

Not all fasting is the same: the amount and type of energy consumed, frequency of eating occasions in a day or number of fasting days per week may vary.

The three types of fasts below have been researched since the 1960s.¹

Ramadan

During the month-long, religious obligation during the Islamic calendar, Muslims adhere to strict fasting (no food or fluids) from dawn to sunset, some 13—18 hours.

All adult Muslims fast, except those who are ill, travelling, pregnant, breastfeeding or menstruating. Those with chronic medical conditions such as diabetes are not expected to fast but many do.

Research has found Ramadan appears to have positive effects on blood pressure (BP) and blood lipids for those with stable cardiac conditions, metabolic syndrome, hyperlipidaemia and hypertension.²

However, in those with diabetes, daylight fasting increases blood lipids ² and results in higher insulin levels,³ risk of hypoglycaemia ⁴ and deterioration of glycaemic control.⁵ HbA_1c can improve after Ramadan ceases, however.⁵

Patients with diabetes need to monitor their condition during Ramadan and may require assistance with alteration of drug dosage and timing, and dietary counselling.⁶

A small weight loss, around 1kg, is seen in those observing Ramadan but it is normally regained the following month.^7-9 Ulcers and epigastric pain may be more common during this time.¹⁰

Alternate Day Fasting (ADF)

ADF is a dietary pattern with a ‘feed day’ when food and fluids are consumed ad libitum alternated with a ‘fast day’ when only 25% of an individual’s energy requirement is consumed in a 24-hour period. A research group at the University of Illinois at Chicago has been testing the effect of this regime in overweight/obese people since 2009. Overall they have found:

• After 8—12 weeks, around 0.6kg of weight is lost per week and fat mass significantly decreases. ^11-14
• Total and LDL cholesterol and BP are reduced while maintaining HDL. ^11,12
• LDL particle size increases. ^12,14,15
• These effects can be seen with an ADF low-fat (25% of energy), high-carbohydrate (60% of energy), high-fibre (27g) regime or an ADF high-fat (45% of energy), lower carbohydrate (40% of energy), high-fibre (27g) regime.¹⁶ Improvements in endothelial function are only seen with ADF low-fat regimes.¹⁷
• Adipose tissue hormones change: adiponectin increases while leptin decreases. ¹⁸
• Compliance with this eating plan is around 85—95%.^11,15
• While ADF is providing interesting results, longer and larger trials are needed to confirm these results.

Intermittent Fasting (IF)

IF is a modified version of ADF where, on two non-consecutive days a week, only 25% of energy requirements are consumed, leaving five days of ad libitum diet.

Made popular by the recent book The Fast Diet by UK journalists Dr Michael Mosley and Mimi Spencer, IF has been researched by the University Hospital of South Manchester.²⁰

Over six months 53 obese, premenopausal women followed an IF regime with two days consuming ~2700kJ/day and five days their habitual diet with usual exercise, compared to 54 women on a chronic energy restriction (CER) diet of ~6276 kJ/day for seven days a week.

• 34% of IF participants lost more than 10% of initial body weight compared to 22% in the CER group.
• Both groups had comparable body fat loss and reductions in C-reactive protein, oxidative stress markers, total and LDL cholesterol, triglycerides and systolic and diastolic BP.
• Both groups saw improvements in fasting insulin and insulin sensitivity but greatest in IF group and no differences in blood glucose.
• As with most diets, compliance with the IF regime was high in the first month (70%) but decreased over time to 64% at six months compared to 55% at six months for the CER group.

Other researchers have studied similar IF patterns but only over 12 weeks with similar results for weight and insulin, cholesterol and glycaemic control.^21-23

Although compliance was not as high, like ADF, IF may be an alternative dieting regime that may work for some patients.

Summary

• Reducing calories in any form assists with weight loss.
• If overweight/obese patients with cardiovascular risks are struggling to lose weight, Alternate Day or Intermittent Fasting may be dietary options worth exploring with medical and dietetic supervision.
• Patients with diabetes may require assistance during Ramadan with glucose monitoring and drug dosage.