Fasting diets come in various flavours, with proponents of this dietary approach advocating for its use for the potential weight-loss and health-promoting benefits. But there are detractors who caution against fasting.
“Fasting has been around for centuries, be it for religious or cultural reasons. However, only recently has mainstream society embraced it as a modern eating practise,” explains Vanessa de Ascencao, a nutritional consultant who holds a Master’s of Science in Nutrition.
Fasting diets defined
At the core, the principles that govern fasting diets typically refer to an eating pattern that limits or controls how many calories you eat and when you eat your meals.
Basically, fasting involves purposefully manipulating your food and drink intake over a set period of time. There are different approaches than just the uninterrupted calorie restriction that most people associate with traditional fasting, which can go on for days.
For instance, intermittent fasting requires that adherents simply limit their food intake to certain periods or ‘windows’ during the day or on certain days of the week to mimic the effect that fasting has on the body.
This approach could entail abstaining from eating for 15-18 hours to skip a meal or two every day, or requires two-day weekly ‘fasts’ that limit energy intakes to 500-600 calories a day.
In its more commercial forms, intermittent fasting techniques go by several names, including the FastDiet, the 5:2 Diet, the Mosley Diet or the Warrior diet.
While previous research and modern societal norms have fuelled the notion that fasting can slow down your metabolism, more recent research affirms that short-term intermittent fasting does not have a detrimental impact on your metabolism.
Rather, it appears that long-term fasting for 48 hours or more has more of a negative effect. And rather than follow this approach indefinitely, most experts recommend periodic, strategically-planned fasts to derive the greatest weight-loss and health benefits.
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The fasting mechanism
When you fast for 12 hours or more, your body has an opportunity to reset its natural hormonal response and, eventually, restore optimal function.
For example, by limiting those constant glucose spikes, intermittent fasting helps to improve your insulin response by reducing the amount of this hormone that your pancreas needs to produce. It also resets insulin receptor sensitivity.
Studies conducted on animals and people tend to show that those who live longer than average all tend to have low insulin levels, presumably because their cells are more sensitive to the hormone and therefore need less of it to function properly.
Vanessa explains that, in general, the 3 mechanisms by which fasting benefits your body include:
- Improved insulin sensitivity and mitochondrial energy efficiency – This approach can retard the ageing process and prevents the onset of various diseases that are typically associated with a loss of insulin sensitivity and a decline in mitochondrial energy.
- Reduced oxidative stress – Fasting can decrease the accumulation of oxidative free radicals in cells, thereby preventing oxidative damage to the cellular proteins, lipids and nucleic acids associated with ageing and disease.
- Increased capacity to resist stress, disease and ageing – Fasting induces a cellular stress response similar to that induced by exercise whereby cells up-regulate the gene expression that increases the capacity to cope with stress, resist disease and slow the ageing process.
Intermittent fasting guidelines:
- Alternate days of normal and restricted calorie consumption, or use the popular 5:2 strategy, which requires ‘fasting’for two days a week, interspersed with five days of normal eating.
- Abstain from eating for 15-18 hours to skip a meal or two on fasting days.
- Choose healthy, nutrient-dense foods and minimise your carb intake by replacing them with healthy fats. Follow this approach on fasting and normal meal days.
- Work your way up to 15-18 hour fasts if your normal schedule included multiple meals a day.
Author: Pedro van Gaalen
When he’s not writing about sport or health and fitness, Pedro is probably out training for his next marathon or ultra-marathon. He’s worked as a fitness professional and as a marketing and comms expert. He now combines his passions in his role as managing editor at Fitness magazine.