Intermittent fasting: does it work for weight loss?

Intermittent fasting: does it work for weight loss?

It's perhaps unlikely that our ancestors ate three meals per day plus snacks. Millennia ago, food scarcity was common, and it created circumstances that led to unintentional periods of fasting. Fasting has also been a part of many religions for centuries. It is quite common for some people to fast to lose weight before a special occasion such as a wedding or a class reunion. But can fasting be the answer to losing weight more efficiently than other weight loss methods?

What is intermittent fasting?

Today, fasting is generally defined as the abstinence from some or all food or drink, or both, for a specified period of time. Intermittent fasting took off as a weight-loss craze in 2012 when British journalists Michael Mosley and Mimi Spencer published their book: the FastDiet. Since then, extensive research has been done regarding the use of intermittent fasting for weight loss.

Today, there are 2 popular methods of fasting:

1) 5:2 fasting:
- Two days per week you limit yourself to less than 2000 kJ if you're female, and 2500 kJ if you're male and the remaining five days you eat as you normally would.

2) 16:8 fasting:
- Food is only consumed between 10 am and 6pm at least 5 days per week

Potential benefits of fasting

Like other calorie restricted diets, intermittent fasting may lead to:
- Reduced blood lipids
- Reduced insulin levels
- Reduced fat mass
- Minor muscle loss
- Reduced blood pressure
- Decreased inflammatory protein markers
*Keep in mind that the research is still in its early stages. Many of the studies were small, short in duration or conducted in animals.

How does it work?

When you fast, human growth hormone levels go up and insulin levels go down. It increases the release of the fat burning hormone norepinephrine. Your body's cells also change the expression of genes and initiate important cellular repair processes.

What does science say?

There is no evidence to suggest that intermittent fasting is any more or less effective than other calorie-restricted diets on weight loss or metabolic health markers such as blood glucose, cholesterol, and insulin levels. There is also insufficient data on the effects of intermittent fasting on sleep and physical activity, which are other important health markers.

Who might benefit from fasting?

Intermittent fasting is not something that anyone needs to do. Fasting may be a viable weight loss option for obese individuals who can't stick to a daily calorie restriction. Even so, there are downsides to fasting-extreme hunger, headaches, and a possible drop in blood sugar.

Who should not do intermittent fasting?

- Persons with diabetes and hypoglycemia
- Eating disorders that involve unhealthy self-restriction (anorexia or bulimia nervosa)
- Use of medications that require food intake
- Active growth stage, such as in adolescents
- Are a female who is trying to conceive
- Are a female with a history of amenorrhea
- Pregnancy, breastfeeding

It is risky to recommend intermittent fasting because there are still many unanswered questions, like:
- How often and for how long should one fast to see a therapeutic benefit?
- Is this diet safe and beneficial for everyone (e.g., generally healthy population, higher risk individuals with chronic diseases, elderly)?
- What are the long-term effects of intermittent fasting?
- Is there a risk of negatively influencing the dietary behaviors of other family members, especially in children who see their parents abstaining from food and skipping meals?

Should you try intermittent fasting?

Health and well-being is so much more than weight! Mental health, physical health, emotional health, and social health are all equally important. From a nutritional perspective, the fact that intermittent fasting does not focus on what you eat (just when you eat it), is worrisome. At the end of the day, your body still needs enough macronutrients (carbohydrates, fat, and protein) and micronutrients (vitamins and minerals) to function at its best, and what you eat (such as more fruit and vegetables, whole grains, healthy fats and lean proteins) can directly increase or reduce your risk for chronic diseases.

Bottom line

It is unclear that intermittent fasting is superior to other weight loss methods regarding the amount of weight loss, biological changes, compliance, and decreased appetite. Certain people who typically eat one or two meals a day or do not eat for long stretches of time may show better compliance with this type of diet. If you need to eat something small every two hours, fasting might not be for you.
More high-quality studies including randomized controlled trials with follow-up of greater than one year are needed to show a direct effect and the possible benefits of intermittent fasting. Strong recommendations on intermittent fasting for weight loss cannot be made at this time.

A final word

Ultimately, you must decide what works best for you. If intermittent fasting is an effective, sustainable diet which you can follow safely and fits well into your lifestyle, then go right ahead! But if intermittent fasting is unsustainable, affects your health, or is socially isolating - it's likely not a good fit for you. If you are interested in incorporating intermittent fasting into your routine, consult with a registered dietitian to ensure you are doing it safely and correctly, rather than attempting it on your own.

1. Diet review: Intermittent fasting for weight loss.
2. Is Fasting Healthy? (PEN)
3. 1. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2017;39:46-58.
4. Intermittent Fasting 101 - The Ultimate Beginner's Guide. Authority nutrition.

Claudine Ryan, Registered Dietitian, RD (SA)

Written by : Claudine Ryan, Registered Dietitian, RD (SA)

Claudine Ryan holds a Bachelor of Science degree in Dietetics and is registered with the Health Professions Council of South Africa. Claudine is passionate about people and their health, and enjoys helping others to optimise their health and manage their chronic lifestyle related diseases through sound nutritional therapy and practical advice.