5:2 Intermittent Fasting vs Traditional Dieting: New Year-Long Study

5:2 intermittent fasting vs traditional dieting. This is what a small research team at the Oslo University Hospital in Norway sought to compare in a new year-long study which was published in the Journal of Nutrition, Metabolism and Cardiovascular Diseases.

More specifically, the researchers compared the effects of two different dietary approaches:

• 5:2 intermittent fasting (a form of whole day fasting), and
• daily caloric restriction (i.e. traditional dieting)

on weight loss and weight maintenance, as well as on other cardiometabolic risk factors.

Before looking at the study, however, let’s briefly look at what intermittent fasting and 5:2 fasting are.

Intermittent fasting and 5:2 fasting

Intermittent fasting is, essentially, an eating pattern which involves alternating periods of little or no energy intake (i.e. caloric restriction) with intervening periods of normal food intake, on a recurring basis.

5:2 fasting involves 2 days of fasting or very low calorie periods per week, with the remaining days of the week eating ad libitum or at maintenance, and falls under what is known as whole day fasting (WDF) which, in turn, is one type of intermittent fasting.

According to research, there are three different types of intermittent fasting:

• Alternate day fasting (ADF), which involves a 24-hour fasting or very low calorie period, alternated with a 24-hour ad libitum eating period.
• Whole day fasting (WDF), which, as mentioned above, usually involves 1-2 days of fasting or very low calorie periods per week, with the remaining days of the week eating at maintenance – this is where the 5:2 the intermittent fasting approach used in this study falls under.
• Time-restricted feeding (TRF), which involves a fasting period of 16–20 hours and a feeding period of 4–8 hours daily, and includes the Leangains protocol by Martin Berkhan.

Takeaway points:

Intermittent fasting (IF) is an eating pattern which involves alternating periods of little or no energy intake with intervening periods of normal food intake, and includes alternate day fasting (ADF), whole day fasting (WDF) and time restricted feeding (TRF).

5:2 fasting involves 2 days of fasting or very low calorie periods per week, with the remaining days of the week eating ad libitum or at maintenance, and falls under what is known as whole day fasting (WDF).

Intermittent fasting vs traditional dieting

The obesity epidemic has become a severe public health crisis. Energy restriction is, of course, the fundamental principle by which people achieve and maintain a healthy body weight since, in line with the First Law of Thermodynamics, fat loss is the result of a sustained negative balance between energy intake and output.

However, while it is usually recommended that people should reduce their calorie intake consistently on a daily basis, many people find it difficult to adhere to diets that involve daily energy restriction.

More recently, intermittent fasting has become popular among people who are looking to lose weight and fat, and even among those who are trying to build muscle and optimize their body composition, partly because of the idea that intermittent fasting may improve dietary adherence.

Indeed, a number of studies, such as this one, this one and this one, on intermittent fasting vs traditional dieting suggest that the two dietary approaches result in identical outcomes in terms of body weight and body fat reduction when calories and protein are controlled for.

Moreover, two recent systematic reviews and meta analyses (this one by Headland et al and this one by Harris et al) also seem to confirm the above results, with both of them concluding that neither intermittent fasting nor continuous caloric restriction was superior than the other for weight loss.

Until recently, however, trials on intermittent fasting vs traditional dieting were short-term, usually lasting 12 weeks, highlighting the need for longer-term studies to be performed.

And this is where this year-long intermittent fasting vs traditional dieting trial by Sundfor et al comes in!

Takeaway points:

Since fat loss is the result of a sustained caloric deficit, caloric restriction is required for weight and fat loss.

While it is usually recommended that people should reduce their calorie intake consistently on a daily basis, many people find it difficult to adhere to diets that involve daily energy restriction.

Research suggests that intermittent fasting may be an effective way to improve adherence to a hypocaloric diet, however, studies are mostly limited to short-term trials.

What the researchers did

Subjects and dietary approaches

The researchers recruited 112 subjects (56 males and 56 females) between 21 and 70 years old, all with obesity and metabolic disease, and randomly assigned them to one of two groups:

1. the intermittent fasting group: subjects were instructed to consume 400-600 kcal on two non-consecutive days a week and to consume food as usual the remaining five days a week. On their fasting/low calorie days, they were given the choice of consuming one meal providing 400-600 kcal, or splitting their assigned calorie intake for the day into two snacks of 200-300 kcal or three snacks of 100-150 kcal.

2. the daily caloric restriction group: subjects were instructed to reduce their energy intake evenly seven days a week so the total weekly energy reduction was equivalent in both groups.

All participants received personalized meal plans, educational materials and behavioral counselling sessions, and were encouraged to follow the general principles of a Mediterranean type diet, emphasizing more vegetables, fruits, legumes, fish, poultry, nuts, fermented dairy products, and olive oil, and restricting processed meats, red meat and sweets.

Study length

The total duration of the trial was one year, consisting of a 6-month weight-loss phase and a 6-month weight-maintenance phase with a pre-planned weigh-in at 12 months.

Measurements

Body weight, waist and hip circumference, and blood pressure were measured following a 10-hour fast at the start of the study, and then at three, six and 12 months.

Food intake and dietary adherence were assessed at the start of the study and after three months using 7-day food records.

Ratings of well-being, hunger and overeating were measured at three, six and 12 months using a subjective Visual Analogue Scale with a numeric rating from 1 (to a small degree) to 10 (to a very high degree).

Blood samples were taken following a minimum of a 10-hour fast at three, six and 12 months.

All participants filled out the self-administered International Physical Activity Questionnaire at baseline and after three months, and were instructed not to change their physical activity habits throughout the trial. Moreover, a subgroup consisting of the first 24 participants wore an accelerometer for seven consecutive days at baseline and after three months, and had their Resting Metabolic Rate (RMR) measured by indirect calorimetry.

Takeaway points:

The researchers recruited 112 subjects (56 males and 56 females) between 21 and 70 years old, all with obesity and metabolic disease, and randomly assigned them to one of two groups: the 5:2 intermittent fasting group or the daily caloric restriction group.

The total duration of the trial was one year, consisting of a 6-month weight-loss phase and a 6-month weight-maintenance phase with a pre-planned weigh-in at 12 months.

A number of outcomes were measured, including body weight, waist and hip circumference, dietary intake and adherence, physical activity, well-being, hunger, and other cardiometabolic risk factors.

The results

Dropouts

Considering that this was a year-long trial, dropout rates were unusually low, with only seven of the 112 participants (four in the intermittent fasting group vs three in the traditional dieting group) dropping out of the study. For comparison, research suggests that six to 12 month trials on intermittent fasting vs traditional dieting typically have dropout rates of over 20%.

The small dropout rate may be attributed to the frequent follow-ups and behavioral therapy, as well as to that subjects in the intermittent fasting group were given the choice of splitting their calorie intake on fasting days into smaller snacks.

According to the authors, none of the participants withdrew due to difficulties adhering to the diet.

Caloric intake, physical activity and RMR

Participants reduced their estimated caloric intake by 28% in the intermittent fasting group, and by 26 % in the daily caloric restriction group from baseline to month three.

Physical activity did not change in either group, which means that any observed changes in any of the outcomes were the result of the changes in the diets.

Resting metabolic rate decreased from baseline to month three by an average of 4.9% in the intermittent fasting group and by 6.1% in the daily caloric restriction group, with no statistically significant differences between groups.

The above changes in RMR are important to highlight, as some believe that intermittent fasting results in larger metabolic rate drops than traditional dieting does, while others believe that intermittent fasting can maintain or even increase resting metabolic rate.

Body weight, circumferences and cardiometabolic risk factors

Overall, weight loss was similar among participants in the intermittent fasting vs traditional dieting group after six months (9.1 kg vs 9.4 kg) and after one year (8 kg vs 9 kg), as were changes in waist circumference (8.7 cm vs 9.6 cm) and hip circumference (6.8 cm vs 7.5 cm) after one year, with no between group differences.

Although both groups experienced a small weight regain in the maintenance phase (1.1 kg, or 12%, in the intermittent fasting group vs 0.4 kg, or 4%, in the traditional dieting group) with no between group differences, regain within the intermittent fasting group reached statistical significance.

The very small weight regain in both groups can be considered quite a success since, according to research, weight regain is usually significantly larger (with an average weight regain of 46%) following long-term energy restriction. The authors attributed this to the frequent follow ups during the weight loss phase, to the cognitive behavioral counselling as well as to the pre-planned weigh-in after 12 months.

Improvements in a number of cardiometabolic risk factors were observed, including improvements in blood pressure, triglycerides and HDL cholesterol with no statistically significant differences between groups.

Adverse events, and feelings of hunger and well-being

Although no serious adverse events were reported, more subjects in the intermittent fasting group reported dizziness, mild headache, mild nausea, and temporary sleep disturbance than in the daily caloric restriction group during the first four weeks.

With regards to ratings of overeating and well-being, no between group differences were reported.

However, subjects in the intermittent fasting group reported more hunger than the subjects in the traditional dieting group at three, six and 12 months. This is something worth keeping in mind if you’re considering trying intermittent fasting, since elevated hunger may negatively affect your ability to adhere to your diet in the long-term.

Takeaway points:

Weight loss at six months was similar between the groups, with little weight regain at 12 months, which only reached statistical significance in the intermittent fasting group.

There were improvements in various cardiometabolic risk factors with no differences between groups.

More subjects in the intermittent fasting group reported mild adverse events as well as more hunger.

Conclusions and the big picture

So what are the conclusions and the practical implications of this year-long randomized controlled trial comparing 5:2 intermittent fasting vs traditional dieting?

Well, based on the results, we can conclude that 5:2 intermittent fasting is as effective, but not more effective than daily caloric restriction for weight loss and weight maintenance as well as for improving cardiometabolic risk factors in free-living middle-aged men and women with obesity and metabolic syndrome.

However, 5:2 intermittent fasting can result in increased feelings of hunger relative to traditional dieting (although research suggests that this isn’t always the case) and may potentially create more adverse events, including dizziness, mild headache, mild nausea, and temporary sleep disturbance.

A couple of things that are worth paying special attention to are:

1. the personalized approach taken with regards to the caloric intake of the subjects in the intermittent fasting group on fasting days, where subjects got to choose if they preferred to have their caloric allowance in one, two or three meals.

2. the frequent follow-ups that took place and cognitive behavioral therapy that the subjects received during the weight loss phase.

Both the above likely contributed significantly to the low dropout rates and successful weight loss and maintenance in both groups.

So, like we’ve mentioned before, we think it’s important to highlight that honoring personal preference with regards to macronutrient ratios, meal timing, meal frequency, and so on, as well as paying special attention to educating and continually supporting people during their body recomposition journey, like we do with our Online Fitness Coaching, is vital for long-term success!

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