There is an ever growing global demand for weight loss techniques, diet plans and weight maintenance programs.
I’ve worked with Registered Associate Nutritionist Hamsa Sharrouf to give you all the evidenced based info on Intermittent Fasting.
This blog explains what it is; the different types; health benefits, and the concerns associated with it.
What is Intermittent Fasting (IF)?
IF is the process of cycling in and out of eating and fasting for varying periods (usually for 12 hours or more). It also includes a limited feeding time-window, with or without caloric restriction.
The different types include:
- Time-restricted feeding (TRF): repeated cycles of complete fasting for at least 12 hours per day with ad libitum feeding (you eat when you are hungry and stop when you are full) for the rest of the day. The most common type of TRF is 16:8 (16 hour of fasting and 8 hours of feeding).
- Alternate Day Fasting (ADF): complete fasting for 24 hours followed by ad libitum feeding for 24 hours.
- Modified Alternate Day Fasting: Eating ~500 kcal for a period of 24 hours followed by ad libitum feeding for 24 hours.
- Periodic fasting: Fasting for 1-2 days per week with ad libitum feeding for the remaining days in a 6:1 or 5:2 pattern.
- Religious fasting such as:
- Ramadan month for Muslims (no food or liquids from sunrise to sunset).
- Yom Kippur fast for Jewish (from sunset until the emergence of stars the following day; 25 hours).
- Greek Orthodox fast (avoid consumption of dairy products, eggs and meat for 40 days during the nativity fast, for 48 days during the lent fast and for 15 days during the assumption fast).
- Daniel fast for 10-40 days; involves a vegetarian diet in addition to forbidding refined foods, white flour, preservatives, additives, sweeteners, flavourings, caffeine, and alcohol.
Why has IF become so popular in recent years?
IF doesn’t require calorie counting or food restriction (other than the timing) which can make it a desirable method of dieting for some people. People often say that it makes them feel like they are in control of their food, rather than the other way around. Individuals are free to set their own eating window and make their own food choices within the chosen time frame, making it adaptable to busy schedules or lifestyles. IF can be adapted as a lifestyle rather than a restricted diet that can be followed for a specific time only.
What are the health benefits of IF? What is the evidence?
Current scientific evidence has largely been derived from animal studies (e.g. rats) which makes the benefits harder to extrapolate to humans.
However, although evidence from clinical trials is limited, initial reports indicate that IF could affect weight loss positively for some people.
A systematic review of four studies found that IF was effective for short-term weight loss among normal weight, overweight and people with obesity.
Another study on 16 obese males and females found that alternate day fasting (ADF) resulted in weight loss (~0.68 kg/week) after 8 weeks of intervention with reductions in body fat percentage; total cholesterol, LDL-C cholesterol (‘bad’ cholesterol), and triacylglycerol and thereby an improvement in CHD risk biomarkers. However, HDL-C (‘good’ cholesterol) did not change after intervention.
HDL-C has been shown by others to generally increase in response to exercise training; therefore, incorporating physical activity into the intervention and for longer periods of time is vital. IF was found to also reduce the risk of type 2 diabetes as well as improve the nervous system function via reducing free radical formation.
Are there potential health risks of IF? The evidence?
IF may increase the susceptibility to diseases. For instance, a cross-sectional study found that skipping breakfast, lunch or dinner was significantly associated with increased CVD risk.
Another study found that participants who consumed 1 meal/day had higher systolic blood pressure values compared with participants who had consumed 3 meals/day. This is explained due to circadian rhythm disruption impact (the inner body clock) on blood pressure.
Moreover, the longest and largest trial of alternate-day fasting (ADF) to date, a 1-year, randomized clinical trial that compared the impact of alternate-day fasting with daily calorie restriction on body mass and risk indicators for CVD in 100 obese adults found that ADF was not more sustainable nor superior to daily calorie restriction in weight loss, weight maintenance, or cardio protection. Nevertheless, it is still possible that some obese individuals may still prefer ADF over daily energy restriction.
In the TREAT randomised controlled trial, time-restricted eating was not linked to weight loss or cardiometabolic benefits in a cohort of 116 overweight or obese subjects. In this trial, participants were randomised into two groups; the consistent meal timing (CMT) (3 meals/day); and the time-restricted eating (TRE) (ad libitum from 12:00 pm and 8:00 pm and a complete caloric restriction between 8:00 pm and 12:00 pm the following day). This CRT has concluded after 12 weeks of intervention that, in the absence of other interventions, TRE was not more effective than CMT in weight loss and cardiometabolic outcomes.
In the elderly, IF was found to be linked to an increased risk of CVD, arrhythmia (abnormal heart rate), and stroke. Fluctuations in blood sugar levels may reduce the instability of the body and lead to falls. Also, excessive restriction of calories can cause hormonal dysregulation in males and female.
Research about Ramadan fasting has found that short-term fasting (7 days) did not adversely affect aerobic performance, walking efficiency nor maximum oxygen uptake. However, longer fasting periods may negatively impact exercise performance and motivation. This can be explained due to the impact of the fasting on the circadian rhythm, sleep deprivation, low levels of blood sugar and dehydration.
It should be noted that weight loss generally plateaus in six months, thus focus on weight maintenance after the initial period of weight loss is important by adherence to a low-calorie diet and regular physical activity for a longer period of time.
Who shouldn’t follow the IF diet?
Individuals who are required to eat meals at regular intervals such as those with type 1 diabetes or patients who need to take regular medications, pregnant and breastfeeding women, elderly as well as children shouldn’t fast.
It should be mentioned that some people may experience irritability and other mood disturbances when they practice IF due to the low blood sugar that may occur. When blood sugar is low, it may cause irritation over periods of fasting. This can also lead to anxiety and poor concentration. Also, keep in mind that skipping meals may affect mental health and social life as food is a vital part of social communication and celebration in all cultures.
Intermittent fasting as a weight loss dietary approach was found to controversially affect weight loss and thereby the risk of CVD. Studies that favourably linked IF with CVD outcome has demonstrated that IF application for a period of 6 months resulted in weight loss of 7-9% and reduced biomarkers of CVD, as well as decreasing LDL-C and triglycerides.
By contrast, several studies have shown the negative impact of IF upon CVD risk markers. It has been shown that skipping breakfast, lunch or dinner was significantly linked to poorer cardiovascular health (CVH) due to its impact on lipid profile and blood pressure. This might be due to the link between skipping meals and the circadian clock system and thereby increasing the postprandial glycaemic response.
In conclusion, compared with daily calorie restriction, IF was not more sustainable nor superior in weight loss, weight maintenance or cardio protection. As the research that exists currently is limited, long-term randomised controlled trials are recommended to evaluate IF efficacy. Also, it is important to keep in mind when choosing to fast that we should always aim to eat a balanced diet rich in protein, fibre, fruits and vegetables as well as drinking plenty of fluids.
This blog was contributed by Hamsa Sharrouf. Hamsa has a Bachelor of Science with Honours Nutrition [first class honours] from Liverpool Hope University LHU (class 2020) and was awarded the Aaron Ainger Prize for the Best Performing Student in Nutrition. She also has a BSc [first class] in Agriculture Engineering/ Horticulture and Micropropagation from Damascus University. Hamsa is interested in all aspects of nutrition with a special interest in clinical nutrition and research. She is very proud to have had her first scientific paper published in the “Nutrients Journal” about metabolic syndrome in the elderly. You can also find Hamsa over on Twitter: @Hamsa74967038
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