Intermittent Fasting: What Science Really Says

Intermittent fasting (IF) has been one of the most talked-about dietary trends of the past decade. From Silicon Valley executives to fitness influencers, everyone seems to have an opinion. But what does the peer-reviewed research actually tell us?

The Main Approaches

There are several popular IF protocols. The 16:8 method involves eating within an eight-hour window and fasting for 16 hours. The 5:2 approach means eating normally five days a week and drastically reducing calories on two non-consecutive days. Alternate-day fasting involves cycling between regular eating days and fasting days.

Weight Loss: Promising but Not Magical

A 2023 systematic review in the New England Journal of Medicine found that intermittent fasting produced similar weight loss to continuous calorie restriction over 12 months. The key advantage wasn't burning more fat — it was that some people found it easier to follow than traditional dieting.

However, a 2024 study from the University of Illinois cautioned that skipping breakfast through time-restricted eating led to increased snacking and slightly worse diet quality in some participants.

Metabolic Benefits

Beyond weight, IF shows interesting effects on metabolic markers. Studies consistently show improvements in insulin sensitivity, particularly in people with prediabetes. A 2025 randomized controlled trial found that 16:8 fasting improved HbA1c levels by 0.5% in adults with type 2 diabetes — comparable to some medications.

Brain Health and Longevity

Animal studies have long suggested that caloric restriction extends lifespan. In humans, the evidence is more nuanced. A 2024 study in Nature Aging found that alternate-day fasting activated autophagy — the cellular cleanup process — more effectively than continuous calorie restriction.

Regarding cognitive function, early clinical trials suggest IF may improve memory and executive function in older adults, though larger studies are needed.

Who Should Be Cautious

IF isn't for everyone. People with a history of eating disorders, pregnant or breastfeeding women, children, and those on diabetes medications that can cause hypoglycemia should avoid or carefully manage fasting protocols. Athletes in heavy training may also find their performance suffers.

The Practical Takeaway

Intermittent fasting is a legitimate dietary strategy with real benefits, but it's not superior to other well-designed eating plans. The best diet is the one you can sustain. If eating within a time window helps you make better food choices and control portions, it may work for you. If it leaves you ravenous and bingeing, it's not the right fit.