Intermittent fasting: what's all the hype?

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Dr. Michael Mosley first introduced the 5:2 fasting method on a TV show back in 2012. Since then, fasting has grown in popularity, with many variations in fasting windows and calorie intake. Supporters of fasting highlight its health benefits—which go beyond just weight loss or maintaining a healthy weight. But is one fasting method better than another? Let’s discuss!

Weight Loss

Intermittent fasting can aid weight loss simply because it helps reduce calorie intake. Whether you’re significantly cutting back for two days a week or limiting your eating to an 8-hour window each day, these methods inevitably lead to lower calorie consumption. Research comparing individuals who fasted two days per week versus those who reduced their daily calorie intake by 20% found no significant difference in weight loss. This suggests that intermittent fasting isn’t necessarily better for weight loss than just consistently eating fewer calories each day.

Health Benefits

There are countless studies on intermittent fasting’s effects on rats, showing very promising results. Some human studies have shown similar benefits, particularly in blood pressure and insulin resistance. However, to improve the quality of research, long-term human studies are needed to confirm whether intermittent fasting leads to lasting health benefits and increased longevity.

That said, research suggests intermittent fasting can lead to:

1. Increased insulin sensitivity
2. Lower blood pressure
3. Reduced bad cholesterol levels
4. Better blood sugar control
5. Improved regulation of appetite hormones
6. Increased growth hormone secretion

These factors contribute to a lower risk of chronic diseases such as diabetes and heart disease.

While the evidence supporting intermittent fasting’s health benefits in humans is still developing, there’s little to suggest it’s harmful if done sensibly. If a particular fasting approach fits your lifestyle, it may be worth trying—and you could see multiple health benefits!

Which Fast Is Best?

There are several intermittent fasting methods gaining popularity, but is one more effective than the others?

Here’s a quick overview of the main approaches:

1. 5:2 Fast – The original and well-known fasting method involves eating normally for five days and restricting calories for two days each week. Originally, it was suggested that women consume 500 calories and men 600 calories on fasting days. However, recent recommendations have increased this to 800 calories. There’s also a 'rapid weight loss' phase, advising 800 calories per day for 2–12 weeks. This should only be done with medical supervision.
2. 16:8 – This method requires fasting for 16 hours and eating within an 8-hour window. For example, if you finish dinner by 7 p.m., you wouldn’t eat again until 11 a.m. the next day.
3. Alternate Day Fasting – This involves fasting every other day. Some versions allow up to 500 calories on fasting days, while others require a complete fast.
4. Warrior Diet – This method involves eating only raw fruits and vegetables during the day and having one large meal in the evening within a 4-hour window.

Some fasting methods don’t require strict calorie counting but instead rely on naturally reducing calorie intake over time. The idea is that with fewer eating hours in the day, you’ll consume less food overall. Additionally, it’s difficult to overeat in just one or two meals, making these methods effective for weight loss.

Not all fasting approaches have been extensively studied. Despite its popularity, the 5:2 diet hasn’t been thoroughly researched in humans, especially long-term. Most of its backing comes from studies on rats and the general concept of intermittent fasting, meaning there’s no clear evidence that this specific method is superior to others.

Does Meal Timing Matter?

Research suggests that consuming more calories earlier in the day and gradually reducing intake throughout the evening may be beneficial. One study found that women who ate their largest meal in the morning lost twice as much weight as those who had their largest meal at night. This is thought to be linked to the body's natural circadian rhythm, which influences how food is metabolized.

Another study on prediabetic men found that eating all their calories within an 8-hour window (7 a.m. to 3 p.m.) led to lower blood pressure and increased insulin sensitivity compared to spreading calorie intake over 12 hours.

These findings suggest that meal timing and overall dietary patterns play an important role in weight management and health.

The Bottom Line...

If your goal is to lose weight, intermittent fasting can be effective—but primarily because it reduces calorie intake. A standard calorie-reduction diet can be just as successful. The key is finding an approach that helps you maintain a calorie deficit in a way that works for you. Some people prefer two very strict fasting days per week, while others find that limiting their eating window prevents excessive snacking. Others may prefer a more moderate daily calorie reduction.

Ultimately, sustainability is key. While research suggests that fasting for 16 hours and eating in an early time window (such as 7 a.m. to 3 p.m.) may be optimal for weight loss and health, this isn’t realistic for everyone.

Social and family time often revolves around evening meals, and there’s no need to sacrifice that to be healthy. The most important factors are consuming quality calories, maintaining a healthy weight, and sticking to a regular eating pattern—whatever works best for you. Whether that means moderately reducing your calorie intake daily or following the 16:8 method with a later eating window, you can still benefit from fasting regardless of when it happens.

Takeaway!

Find a fasting approach that fits your lifestyle and is sustainable—this is the key to long-term success.

One final note...

The Nutracheck App has a feature to support the 5:2 diet. You can select your two fasting days and set your calorie target—either 500 or 800 calories. To find the 5:2 diet setting, open the app, tap the blue menu button on your Diary page, then tap Nutrient Goals and select 5:2.