Intermittent Fasting vs. The Mediterranean Diet – What’s Best?

In a previous article we examined the Ketogenic Diet (Keto). Outside of its limited use in clinical settings, Keto meets all the criteria to be considered a ‘fad diet’. At least according to Dietitians Australia that is!

Keto has rigid rules regarding what can and cannot be eaten. It exclusively blames carbohydrates (carbs) for our nutrition-related health and weight issues. It’s also associated with a variety of health risks.

In our Personal Training and Weight Management Coaching programmes we analyse a wide range of popular dietary practices.

As well as Keto, we analyse the increasingly popular Intermittent Fasting (IF) and the well-established Mediterranean diet (MedDiet).

Against the Dietitians Australia criteria, IF and the MedDiet don’t appear faddish. Indeed, the MedDiet is referred to as more of a lifestyle practice. This aligns with Dietitians Australia’s recommendation that:

The best approach to weight loss and health is to follow a long-term, healthy and balanced eating plan… And to keep active.

This recommendation is a position that we advocate throughout our programmes at NZIHF.

With a focus on weight loss, in this article we’ll examine:

• What Intermittent Fasting is and how it works.
• What the Mediterranean diet is and how it works.
• Research into Intermittent Fasting and the Mediterranean diet.
• The shortcomings of both for health and sustainable weight-loss.

What is Intermittent Fasting and how does it work?

The term ‘Intermittent fasting’ (IF) describes dietary practices that involve restricting caloric intake for a set period of time. These periods of restriction are usually cycled with periods of normal or unrestricted intake.

Throughout history, fasting has actually been a common feature of human life. Relying on the seasonal availability of naturally occurring foods, fasting was essentially forced on early hunter-gatherers.

It’s hard to eat at regular times when food simply isn’t available!

The ancient Greeks were great believers in fasting.

Hippocrates, recognised as the ‘father of Western medicine’ stated that:

‘To eat when you are sick is to feed your sickness’.

Fasting has been and continues to be common to many religious practices. For example, throughout the holy month of Ramadan, healthy adult Muslims don’t eat or drink during daylight hours.

Anthropologists note that for the vast majority of human history (approx. 99%) we’ve lived as hunter-gatherers. As such, humans have adapted to survive periods of food scarcity and enforced fasting.

Biologically we’ve developed:

• A digestive system made of smooth elastic muscle which enables us to overeat. This enables us to take full advantage of food when it’s available.
• The capacity to convert and store the excess food we consume as fat which can be used for energy during times of food shortage.

The whole idea of IF is that it encourages the body to access and burn through its fat stores.

There is some sound physiological reasoning behind this.

Via digestion, the foods we eat (in particular carbohydrate-rich foods) are broken down into sugar, or technically ‘blood glucose’. The cells in our body use this blood glucose for energy.

Surplus blood glucose isn’t wasted. It’s either converted into glycogen (stored blood glucose) or fatty acids and stored in our fat cells as bodyfat. Produced by the pancreas, the hormone insulin is instrumental in these processes.

Insulin has many functions. It enables our cells to use blood glucose for immediate energy as well as stimulating the liver to:

• Convert and store excess blood glucose in the form of glycogen.
• Use excess blood glucose to synthesise (make) and store fatty acids.

Insulin is known as a ‘fat-sparing’ hormone. Not only does it stimulate the synthesis of body fat, it protects those fat stores by driving our cells to preferentially use readily available blood glucose for energy.

However, in-between meals and during periods of fasting, insulin levels drop. The absence of insulin enables the energy stored in glycogen and fat cells to be released for use.

The rationale underpinning IF is that it allows insulin levels to drop far enough and for long enough that we can burn off our fat stores.

*Note. Because fasting influences insulin and blood glucose, people with diabetes should always consult their doctor before engaging in IF.

What are the main types of Intermittent Fasting?

There are a wide variety of IF protocols, most of which fit within these categories:

• Whole-day fasting.
• Alternate-day fasting.
• Time-restricted feeding.

1. Whole-day fasting (WDF)

Whole-day fasts usually involve 1-2 days per week of fasting with no food restriction on other days. Some protocols demand strict dieting where only water, tea and/or coffee are allowed (without milk or sugar). Other protocols allow up to 25% of daily caloric needs to be consumed during fasting days.

The most well-known of these fasts is the 5:2 Diet.

For five days of the week, people eat normally. On the remaining 2 days, caloric intake is restricted to 25% of daily energy needs. This restriction equates to approximately 500 calories per day for women, and 600 per day for men.

2. Alternate-day fasting (ADF)

As the name suggests, these types of fasts involve alternating days of food restriction with days of no restriction. For example, I might fast on Monday, Wednesday and Friday and eat normally on Tuesday, Thursday and the weekend.

As with whole-day fasts, some protocols demand strict caloric restriction. Others allow people to consume up to 25% of their daily caloric needs.

3. Time-restricted feeding (TRF)

Time-restricted feeding ties into the day-night cycle that early humans evolved with. Hunting, gathering (and eating) would occur during the day, sleeping would occur during the dark nighttime hours. Advocates of these types of fasts point to research which suggests that eating during nighttime hours is associated with weight gain.

The most popular ‘TRF’ is the 16:8 Diet. This involves fasting for 16 hours and only eating during the remaining 8 hours.

There are more lenient variations such as the 12:12 Diet, or stricter variations such as the 23:1 Diet.

What does the research say about Intermittent Fasting?

Harris et al [ref 1] completed a meta-analysis investigating IF interventions for the treatment of overweight and obesity. Six randomised controlled trials (RCTs) were included in their analysis.

The trials included alternate-day fasting and fasts lasting two (5:2 Diet) or four days per week. They compared IF to a control (normal diet) and those who reduced their daily caloric expenditure by approximately 25%. This group was referred to as ‘continuous energy reduction’ (CR).

For weight loss, the study found that:

• IF was more effective than a normal diet but,
• There was no significant difference between IF and CR.

In 2022 Gu et al [ref 2] completed a meta-analysis of 43 RCTs with 2483 participants. The analysis also compared people on IF with those on a non-intervention (their normal diet) or CR diet. Notably, the CR diets covered in this analysis included the MedDiet.

The study found that:

• IF was more effective than a normal diet at reducing weight, fat mass, waist circumference and blood lipid (fat) levels.
• No significant differences were evident between IF and CR other than IF being slightly better at reducing waist circumference.

An individual study of note was completed by Lin et al [ref 3]. These researchers investigated whether TRF was more effective for weight control and reducing cardiovascular disease than caloric restriction (CR).

Ninety adults with obesity took part in a 12-month RCT. Participants assigned to the TRF protocol were allowed to eat between noon and 8pm only (a 16:8 protocol). Participants assigned to the CR group reduced their daily caloric intake by approximately 25%.

Like the previous studies, the researchers found that…

• TRF and CR were equally effective at producing weight loss!

An important and unanswered question arises here. Is IF effective simply because it produces a significant caloric reduction?

What is the Mediterranean Diet and how does it work?

The Mediterranean Diet (MedDiet) regularly tops the list of diets endorsed by medical and nutritional organisations. It’s described more as a ‘way of eating’ than a regimented diet.

The MedDiet is based on dietary traditions from countries bordering the Mediterranean Sea such as Greece, Crete and Southern Italy. Researchers started examining these traditions in the mid-20th century.

Despite having limited access to healthcare, these countries displayed significantly:

• Lower rates of chronic disease.
• Higher average life expectancy than people following a more ‘Americanised’ diet.

Fundamentally, the MedDiet is a high-fibre, plant-based eating plan. It promotes a daily intake of whole grains, breads, vegetables, fruits, beans, legumes, nuts and seeds.

Several additional factors make the eating plan unique. It:

• Recommends choosing fish and seafood over meat, dairy and poultry as the preferred sources of animal protein.
• Emphasises unsaturated fats from olive oil, nuts, avocados, and oily fish like salmon and sardines, over saturated fats from animal foods.
• Promotes water as the main daily beverage, but also recommends the moderate consumption of wine (1-2 glasses per day).
• Highlights the importance of daily physical activity and the social benefit of eating meals together.

When compared to other popular diets, the MedDiet is somewhat vague. It doesn’t specify portion sizes or amounts of food to eat. It leaves it up to the individual to decide how much to eat at each meal.

It’s worth noting that by prioritising the consumption of unprocessed/lightly processed plant foods, it’s hard to over-consume calories.

The reason being – plant foods tend to be less concentrated sources of energy than animal foods. And the high fibre content of unprocessed plant foods adds ‘calorie-free’ bulk. This aids satiation (the feeling of fullness). It’s the emphasis on high-fibre, unprocessed plant foods that results in the MedDiet being considered a ‘CR’ diet.

What does the research say about the Mediterranean Diet?

Over the years, an abundance of research has accumulated on the MedDiet. Without doubt, it is by far the most studied diet. The mass of data, often summarised in reviews and meta-analyses, paint a clear picture. Here are but two examples:

A review of studies completed in 2015-2016 [ref 4] found that the MedDiet is associated with:

• Increased life expectancy, reduced risk of chronic disease, and improved quality of life and well-being.
• A reduced risk of myocardial infarction (heart attack), stroke, total mortality, heart failure and disability.
• The prevention of cognitive decline and breast cancer.

The authors summarised their findings as such:

In the era of evidence-based medicine, the MedDiet represents the gold standard in preventative medicine, probably because of the harmonic combination of many elements with antioxidant and anti-inflammatory properties, which overwhelm any single nutrient or food item. The whole seems more important than the sum of its parts.

With regard to weight loss, an exhaustive review of MedDiet studies [ref 5] found that:

• In general, the MedDiet is as effective as other diets at producing weight loss.
• In studies with longer intervention periods (6 months +), the MedDiet produces a greater reduction in body weight than other diets.
• Following the MedDiet is associated with a reduced risk of becoming obese over time.

Amongst their summary, the authors noted that:

The MedDiet is a dietary pattern composed of high-quality foods that has been associated with reduced mortality and lower incidence of several chronic NCDs (Non-Communicable Diseases) as well as with similar weight-loss effects as other approaches.

Intermittent Fasting vs. the Mediterranean Diet – which is best?

Compared to more faddish diets (like Keto), IF and the MedDiet appear superior across a variety of health metrics.

In general, they have flexibility built into them. With the exception of the stricter IF versions, they don’t place rigid demands on followers. They don’t demonise certain food groups (e.g., ‘carbs are the enemy). They either already have a significant body of scientific research that supports their use or that body of evidence is building rapidly.

So, which is best? Despite my opinions, I’ll leave that question for you to contemplate.

It’s worth noting though that the MedDiet is evident across the national nutrition guidelines of many countries, including NZ.

Like the MedDiet, our Eating and Activity Guidelines encourage us to:

• Consume more wholegrain cereals, fruit and vegetables.
• Prioritise unsaturated fats from plant sources over saturated fats from animal foods.
• Limit the consumption of animal foods and incorporate/increase our consumption of fish and seafood.
• Engage in daily physical activity.
• Limit the consumption of ‘treat’ foods – junk and fast-food.
• Prioritise drinking water for hydration and consuming alcohol in moderation.

The body of nutritionists, dietitians and public health experts who produce our guidelines, clearly have a view.

It’s also worth remembering that the MedDiet is considered a ‘continuous energy reduction (CR) diet’. Following such a diet is associated with an approximately 25% reduction in daily caloric intake.

As research into IF has revealed, IF is no more or less effective than CR diets. This raises questions such as:

• If fasting is hard to sustain, would people be better off trying to eat more ‘in-line’ with the MedDiet?
• Would IF be more beneficial if it encouraged people to eat in-line with the MedDiet on unrestricted food days?

No matter how effective fasting is, it’s unlikely to completely counter a regular diet high in junk-food.

A final word – what’s missing from IF and the MedDiet?

No matter how good the MedDiet (and IF) may be, they suffer the same flawed assumption of all diets.

They assume that:

People’s behaviour will magically change once they know what and how they should be eating.

Seldom is this the case. People’s behaviour is shaped largely by the environment they live in 24/7.

New Zealand’s current food environment has no resemblance to that of mid-20th century Greece, Crete and Southern Italy. Over the past 30-40 years our food environment has become increasingly Americanised.

Unsurprisingly, our epidemic of overweight and obesity mirrors that of the USA.

We’re swamped by fast-food, junk-food, discount liquor, soft drinks and energy drinks. Media promote these unhealthy ‘food products’ exclusively and exhaustively. As we noted in this article, such products are manufactured to be ‘addictively’ habit-forming.

To eat more in-line with the MedDiet and our national guidelines, people need more than just dietary information. They need non-judgemental support and guidance that enables them to:

• Understand and mitigate the unhealthy aspects of their current food environment.
• Transform unhealthy eating behaviours into healthier behaviours.
• Build and sustain healthy eating and activity behaviours that are impervious to unhealthy influences.

If you’d like to help provide such support and guidance, come and talk to us about becoming a Weight Management Coach. Not only will you learn about nutrition and diet, you’ll:

• Develop a comprehensive understanding of the factors that shape our eating behaviours.
• Learn how unhealthy behaviours are built and how they can be modified.
• Build a practical skill-set that enables you to affect meaningful change in peoples lives.

The change we need isn’t coming from higher up (our ‘leaders’). It’s coming from practitioners that care and are equipped to make a significant difference.

References

1. Harris et al. (2018). Intermittent fasting interventions for treatment of overweight and obesity in adults: A systematic review and meta-analysis. JBI Database of Systematic Reviews and Implementation Reports. https://oce.ovid.com/article/01938924-201802000-00016/HTML
2. Gu et al. (2022). Effects of Intermittent Fasting in humans compared to a non-intervention diet and caloric restriction: A meta-analysis of randomised controlled trials. Frontiers in Nutrition. https://doi.org/10.3389/fnut.2022.871682
3. Lin et al. (2023). Time-restricted eating without calorie counting for weight loss in a racially diverse population. Annals of Internal Medicine. https://doi.org/10.7326/M23-0052
4. Martinez-Gonzalez and Martin-Calvo. (2016). Mediterranean diet and life expectancy; beyond olive oil, fruits, and vegetables. Current Opinion in Clinical Nutrition & Metabolic Care. https://doi.org/10.1097/mco.0000000000000316
5. Dominguez et al. (2023). Mediterranean diet in the management and prevention of obesity. Experimental Gerontology. https://doi.org/10.1016/j.exger.2023.112121