Alternate day fasting(ADF) is a form of intermittent fasting where you alternate feast and fast days. Normally, you eat 25% of your daily calorie needs on fast days and 125% of your calories on feast days. This equates to eating at an average of 75% of your daily calorie needs over the long term.

Suffice it to say, since you are counting calories, calories matter. But does alternate day fasting provide benefit beyond the calorie restriction it creates, and the weight loss that follows? For weight loss, the data is split down the middle. And even in the studies where it is more effective, drop out rates tend to be high.

One paper found no edge for ADF compared to calorie restriction in weight loss, adherence, or weight management in metabolically healthy people. They also noted that people tended to under-eat on the feast days and overeat during the fast days.

Another study found no difference between alternate day fasting and standard calorie restriction over 6 months. This included weight loss and change in measures of blood glucose in people with Type 2 diabetes. Again, the dropout rate was high at ~30%, and the weight loss was marginal.

But a more recent paper found that ADF was more effective than daily caloric restriction at improving blood glucose regulation. They found substantial improvements in fasting insulin and insulin resistance over 12 months. This, despite leading to similar levels of weight loss.

If you read our blog last week on the cause of Type 2 diabetes in obese people, this flies in the face of those results. Check out that blog here.

Let’s dig into this paper and see if it proves that ADF is a superior option to daily caloric restriction for improving insulin resistance.

Alternate day fasting: Sticking to the plan

Before we dive into the results of this study, it’s important to first look at compliance and the practical applications. As with essentially all studies on weight loss, there was a significant number of dropouts. In the ADF group, 35% of the subjects dropped out while in the daily caloric restriction, 19% dropped out.

This is an important consideration. Even if a dietary approach is effective, if people don’t stick to it, it won’t be effective for them. Despite a high dropout rate for both groups, there was a substantial drop in body weight in those who stuck around.

People in the ADF group lost 8% of their bodyweight(~18lbs); those in the daily restriction group lost 6%(~11lbs). This is actually much better weight loss than typically seen in other ADF studies. But, the devil is in the details.

The studies mentioned above showing no weight loss with ADF didn’t provide the same level of dietary support as this one. First, all meals were provided to both groups for the first 3 months in this study. The other studies gave the participants caloric targets to hit.

Furthermore, during months 4-6, all participants received weekly nutritional counseling. This is important because it increases adherence for those participants who stick around.

During months 6-12, both groups were to maintain their weight loss. In the daily restriction group, participants ate 100% of their calorie needs every day. In the ADF group, fast days were 50% of calorie needs and feast days were 150% of calorie needs.

With meals provided and an additional 2 months of nutritional support, ADF led to greater weight loss than daily caloric restriction, though it was not statistically significant. Based on this data, we’d expect measures of insulin resistance to be similar between the 2 groups.

Alternate day fasting vs daily caloric restriction: Measures of insulin resistance

While the weight loss between groups was not statistically significant, there was quite a difference in measures of insulin resistance. In the ADF group, fasting insulin dropped by 52% and insulin resistance as measured by HOMA-IR by 53%. In the daily restriction group, fasting insulin dropped by 14% and HOMA-IR by 17%.

This is great! An added bonus is that the bloodwork was conducted 12 hours after the last meal for each group, and after feast days in the ADF group. So the lower fasting and insulin resistance wasn’t a product of coming off a fasting day.

Overall, this provides some compelling support that alternate day fasting may be more effective than daily energy restriction for improving insulin sensitivity. But does this mean it’s better for Type 2 diabetes?

There are a couple of potential issues here. The participants in this study were insulin resistant, but negative for Type 2 diabetes. This makes it difficult to apply this data to people with overt Type 2 diabetes.

Another issue is that the ADF group again ate significantly fewer calories on feast days and significantly more on fast days.The daily restriction group was much more on target in hitting their calorie goals. This may explain the better weight loss.

Finally, though the weight loss difference between the groups was not statistically significant, it is in a range that would be clinically significant. If you read last week’s blog, we mentioned that losing just 10% of your weight can put Type 2 diabetes into remission.

It simply could be that ADF got people closer to that magical 10% number and, therefore, improved fasting insulin and HOMA-IR more by causing more weight loss. It’s important to point out that both groups still had some level of insulin resistance.

But the ADF group had borderline insulin resistance while the daily calorie restriction group had significant insulin resistance. This jibes with the notion that 10% is the magic number for weight loss to reverse insulin resistance.

Is ADF right for you?

So, what does this paper as well as the other papers on alternate day fasting tell us about its effect on insulin resistance? Well, first, it doesn’t seem to have any effect on metabolically healthy people. Additionally, the improvements in insulin resistance require weight loss, which requires a caloric deficit.

Furthermore, there is generally low adherence, which is true for all diets and an important consideration. Some people just vibe better with different dietary approaches. Some like Keto, some like intermittent fasting, and some do great with 5 meals a day omnivore.

You’ll find, as you work with people to help them lose weight, that they’re very much a mosaic in terms of what works for them. In terms of building health, nothing trumps maintaining a healthy weight, aside from maybe exercise.

If a person simply cannot control their weight eating a standard omnivorous diet, it’s probably not a great strategy for them

If a person can’t stick to 3 meals per day without overeating, IF is probably not a great strategy for them.

As a general principle, identifying the appropriate dietary approach for an individual takes time and normally requires working with someone. That’s why programs like Virta health and the approach in this study typically get far better results than just telling people to hit a calorie target or follow some basic approach.

Conclusion

Alternate day fasting is becoming increasingly popular as a means of losing weight and improving glycemic control in those with insulin resistance. As with other approaches, weight loss seems to be at the center of improvements in insulin sensitivity.

A recent paper found that ADF led to substantially better insulin sensitivity compared to daily caloric restriction, despite similar levels of weight loss. It’s important to point out that though the results were not statistically significant, they were likely clinically significant. This is based on the idea that 10% weight loss puts Type 2 diabetes into remission.

For those who can stick to it, ADF is a viable approach for improving insulin resistance. It may outperform daily calorie restriction in obese people with insulin resistance but free of Type 2 diabetes. However, based on all the data, weight loss is essential to these improvements.

Anecdotally, we see improved ability to manage hunger in those who thrive under intermittent fasting protocols. However, this may be selection bias in that people who better manage hunger may be attracted to ADF. Whether you choose ADF or another dietary approach, consulting with a health coach may be essential to adherence, and thus, success.