Honed the holy grail of fat loss and a health elixir for countless ailments, Intermittent Fasting (IF) is taking first place in the race of the latest fad diet, but just how healthy is it?
What is IF?
A fast is when you go a significant length of time without eating. How long depends on your choice. In the science world, anything over 12 hours is considered a fast. Time-restricted eating plans involve eating within certain hours, for example, between 10 am and 6 pm for a 16-hour fast. More intense plans are called the 5:2 approach, where you eat "normally" for five days a week and for the other two, you dramatically restrict your diet and cut calories by over 75% - for example, if you eat 2,000 calories a day, for two of those days you only eat 500. Finally, alternate days fasting involves a 24-hour fast once weekly or monthly.
What are the benefits?
Healthcare “experts” on podcasts and blogs will tell you that IF is the reason for their weight loss, lower cholesterol, lower blood pressure, improved blood sugar, less inflammation, better brain health, fewer age-related diseases, and even go as far as saying you’ll live a longer life. Experts say the diet works by allowing people to eat whatever they want as long as it’s within a narrow timeframe. In turn, they eat fewer calories overall.
The reality
Most research on IF has been conducted on animals and men in small studies of relatively short duration focussing on the 5:2 diet. A recent analysis of over 20,000 U.S. adults found that people who limited eating to less than 8 hours a day were 91% more likely to die from cardiovascular disease compared to people who ate across 12-16 hours per day and showed no associations with living longer.
IF for weight loss?
In 2020, a rigorous three-month study found that people lost little weight with IF. The study assigned overweight adults to a 16-hour fast, only consuming meals between noon and 8 pm. Over the three months, participants lost an average of two to three and a half pounds, primarily from lean mass (muscle*) - only half a pound more than the control group. Sixty-five per cent of the weight lost in the fasting group was from lean mass - more than double what is considered normal for weight loss. No other benefits were reported.
*Why is muscle so important? Muscle protects the skeleton and organs and preserves bone density, joint health and overall mobility - especially as we age. Increased muscle mass is also linked to lower mortality and increased metabolism by burning calories at rest.
Skipping meals and binge eating
Due to social requirements, IF usually involves no breakfast and an early dinner. However, as the old adage goes: ‘eat breakfast like a King’ still reigns. Studies have consistently found that overweight adults lose more weight and improve their cardiovascular health when they eat a large breakfast, modest lunch and light dinner compared to a small breakfast and big dinner. Why is this?
Well, have you ever gone for too long without eating? How do you feel? Miserable? Irritable? More receptive to stress? When you finally set sights on some food, do you ravage through it like a starved dog - often opting for the high-sugar, high-carb options?
Skipping meals has proven to negatively impact blood sugar levels, resulting in humans choosing highly processed foods to self-soothe, but ultimately, make us feel more uncomfortable afterwards.
One study found that skipping breakfast is associated with lower diet quality and higher consumption of snacks and carbohydrates in the afternoon and evening. While total daily energy intakes were similar between children who ate breakfast and those who didn’t, the Breakfast skippers' mean BMI was higher. In conclusion, it’s not the act of skipping breakfast that has negative side effects, it’s the behavioural traits as a result.
As Stephanie Mara Fox, Somatic Nutritional Counselor, says, “Rhythmic, consistent eating can stabilise your blood sugar levels, support your stress response, help with navigating emotions easier, and provide a general sense of calm and stability. Eating at similar times in the day can support your body with relaxing and trusting that it is going to be nourished moving you out of a fight or flight response and into rest and digest mode where you will more easily assimilate your food, decreasing the likelihood of a binge later in the evening. Eating within an hour of waking up will stoke your metabolic fire, actually supporting you in losing and maintaining your weight.”
Dr Frank Hu, chair of the Department of Nutrition at the Harvard T.H. Chan School of Public Health, explained that humans have a biological desire to overreact to post-fasting periods as the appetite hormone and hunger centre in the brain goes into overdrive. Dr Hu concluded, “there's no strong evidence that fasting adds health benefits beyond any other weight-loss strategy.”
Psychological side effects of IF
IF may cause psychological effects, including increased stress and anxiety around food and eating, leading to disordered eating patterns and exacerbated body image issues (read my article on BDD). A study conducted by The University of Toronto analysed data from nearly 3,000 adolescents and young adults by the Canadian Study of Adolescent Health Behaviours. The results showed that in addition to binge eating, IF led to compensatory behaviours such as vomiting, laxative use, and compulsive exercise in both men and women.
IF impact on women, fertility and hormone health
Medical centres advise that the following groups of people should not try intermittent fasting:
Anyone with a history of an eating disorder.
Anyone who is underweight or malnourished.
Pregnant women.
Women who are breastfeeding.
Children.
Anyone trying to get pregnant
Research suggests that fasting can disrupt hormone levels and metabolic health as women appear to be more sensitive to changes in calorie intake and fasting periods. This is due to a molecule called Kisspeptin which controls an integral part of the reproductive pathway. It is sensitive to insulin and leptin, which help women regulate hunger and satiety signalling, which gets suppressed during fasting.
Although research is limited, some studies involving rodents reported changes in oestrogen levels which negatively affected reproductive functions, including hormonal imbalances, irregular periods, fertility, pregnancy, and lactation issues. When the hypothalamus believes the body is under physical or mental stress, it delays ovulation until the stress has passed. Unfortunately, the body cannot determine whether the stress is circumstance (drought/starvation) or self-inflicted (limiting calories). Our primary stress hormone, cortisol, then becomes “dramatically elevated” during fasting, which is associated with weight gain, muscle weakness, high blood sugar and pressure, excessive hair growth and weak bones.
The thyroid produces hormones and affects every organ in the body. It is located in the neck and governs the body’s energy levels. According to Sara Gottfried, M.D., author of Women, Food and Hormones, the lack of carbohydrates experienced during fasting affects the thyroid specifically. “Women need carbs for their thyroid. Carb restriction can affect levels of the thyroid hormone reverse T3, which provides a mechanism to slow down metabolism to save energy.”
Another study investigating DHEA levels (an adrenal hormone responsible for producing sex hormones, including egg production) found that fasting could decrease DHEA levels in pre and post-menopausal women. So, if you’re intermittent fasting and notice changes in your period, this is a sign that you’re overdoing it! However, for optimal hormone functioning, the body must receive balanced, complete meals with adequate fats, proteins, minerals, and vitamins. Fasting is one thing, but how you break it is another.
Conclusion: Glamorised calorie restriction
Many diet trends have origins in legitimate science but often get distorted by the time they reach mainstream audiences. Benefits become exaggerated. Risks get downplayed, and highly detailed reports get reduced to a caption. As Roger Collier says: “science takes a back seat to marketing."
“I find it fascinating that this diet has become so popular and there are so few studies," says Dr Krista Varady, a professor of nutrition at the University of Illinois, Chicago, said in The New York Times. Bold claims about increasing longevity and decreasing cancers are, so far, baseless. There have been no proof of improved survival or delayed tumour growth in mice, anyway - which we know is insufficient.
In reality, IF is a spin on calorie restriction - which is the only consistently proven approach to weight loss. It’s boring, I know. Cutting calories requires discipline, planning and careful consideration, which few humans like to engage with these days. It's why IF is so attractive: in premise, eat whatever you want, just not during certain hours. However, it neglects to consider what you eat and the consequence of long durations of starvation.
If you are looking for a way to kickstart your weight loss journey, then maybe intermittent fasting can be a method to create a calorie deficit in the short term, but it does not work for everyone. I recommend macro tracking first to understand what types of food you should be eating to support your hormone profile and training and lifestyle needs - especially if you are a women, and one that would like healthy fertility, too.
Now go eat breakfast and stop starving yourself!!!