Insulin resistance and the Mediterranean diet

The inflammation-lowering effect is more positive news about this diet.

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With insulin resistance now implicated in many conditions, including Type 2 diabetes, Alzheimer’s disease and polycystic ovarian syndrome, dietary management of the condition is the subject of much interest and research.

Benefits of the Mediterranean Diet

While low-carbohydrate and low-fat diets have been shown to be effective in weight loss, the focus on what to avoid often makes them unpopular. Advice to lose weight is often heard with a sense of foreboding. Seventy-three percent¹ of patients with a BMI of over 30 have tried to lose weight in the previous 10 years, and research shows that those who attempt weight loss have tried, on average, over seven times². Indeed, even well-run research studies show that even if patients are successful in losing weight, most of the loss is typically regained by 12 months.

In contrast to low-carbohydrate or low-fat diets, a focus on diet quality, and foods to include, is often more appealing. The Mediterranean diet has excellent evidence for improving HbA1c and insulin sensitivity. Even following Mediterranean dietary interventions that do not limit kilojoules or carbohydrate quantities improves HbA1c from an average of 7.1% to 6.8%³, and reduces the risk of T2DM by 35%⁴.

Mechanisms of the Mediterranean diet

The cause of insulin resistance is multifactorial, but chronic low-level inflammation has been shown to be a key component⁵. The mechanism of action of the traditional Mediterranean diet is thought to be through the diet’s anti-inflammatory components. There are a variety of traditional diets that fit this category, rather, they are all rich in antioxidants, in particular, vitamins A, C and E, polyphenols and carotenoids.

The high amount of fibre in the diet not only regulates the rise of blood glucose levels, but also produces short-chain fatty acids in the large intestine, which have anti-inflammatory effects after absorption.

Finally, the high proportion of omega 3s and mono-unsaturated fats – from seafood, nuts, olive oil, and avocadoes – also appears to reduce inflammation^6,7.

There is no one definition of “The Mediterranean diet”, however, the PREDIMED trial uses a simple 14-item, validated questionnaire of adherence (see Box 1) which provides a quick checklist to go through during the consultation. While much of the information is fairly typical of healthy eating advice – e.g. eating less animal fats, red meat, soft drinks and sweets – it also provides guidance on what to eat instead. 

Patients can be discouraged by a list of foods not to eat, and appreciate advice of what they can increase. They can believe that almost all foods have been declared “unhealthy” and are relaxed by the advice to increase their intake of foods such as fruit, nuts, and olive oil. The inclusion of these palatable foods increases compliance. Patient feedback after adopting the Mediterranean diet has shown that people, in general found the diet to be simple to follow, with good amounts of variety, and the concept of “Mediterranean” diet to be appealing⁸.

Removing barriers to adopting the Mediterranean diet

The concept of a “diet” may be a barrier to some, conjuring thoughts of restriction and avoiding delicious food. Presenting the Mediterranean diet as a Mediterranean lifestyle may be more acceptable and has the benefit of highlighting the importance of enjoyable, regular physical activity throughout the day, and social connections. Additionally, regular blood tests showing biochemical improvement may boost motivation.

Factors found to be helpful in encouraging the adoption of the Mediterranean diet include:

Further increasing patients’ knowledge, motivation and acceptance may be achieved by patients attending a cooking class with a family member. A referral to a dietitian can be helpful for patients whose health is being impacted by insulin resistance and who are in need of further assistance and support with dietary advice.

Box 1. PREDIMED validated diet questionnaire and suggestions for use (in italics). The PREDIMED trial was a randomised control trial comparing a standard low fat diet to a Mediterranean diet supplemented with either nuts or olive oil. A score of 10 or over shows good adherence.

Questions	Criteria for 1 point
1. Do you use olive oil as your main culinary fat?	Yes
2. How much olive oil do you consume in a given day (including oil used for frying, salads, out-of-house meals, etc)?	?4tbsp
3. How many vegetables servings do you consume per day (1 serving: 200g (consider side dishes as half a serving))	?2
4. How many fruit units (including natural fruit juices) do you consume per day?	?3
5. How many servings of red meat, hamburger or meat products (ham, sausage, etc.) do you consume per day (1 serving: 100-150g)	<1
6. How many servings of butter, margarine, or cream do you consume per day (1 serving: 12g) *Olive oil spread has not been fully evaluated for health effects	<1
7. How many sweet or carbonated drinks do you drink per day? *not including 100% fruit juice	<1
8. How much wine do you drink per week? *The traditional Mediterranean diet includes 1-2 glasses of red wine per day taken with meals, benefits appear to be an effect of polyphenols and alcohol.	7-14 glasses
9. How many servings of legumes do you consume per week? (1 serving: 150g)	?3
10. How many servings of fish or shellfish do you consume per week? (1 serving 100-150g of fish, or 200g of shellfish)	?3
11. How many times per week do you consume commercial sweets or pastries (not homemade), such as cakes, cookies, biscuits or custard?	<3
12. How many servings of nuts (including peanuts) do you consume per week? (1 serving 30g)	?3
13. Do you preferentially consume chicken, turkey, or rabbit meat instead of veal, pork, hamburger, or sausage? *lean red meat or pork 3-4 times per week have been shown to have minimal impact on the effectiveness of the diet.	Yes
14. How many times per week do you consume vegetables, pasta, rice or other dishes seasoned with sofrito (sauce made with tomato and onion, leek, or garlic and simmered with olive oil)?	?2

Jessica Bailes is a senior dietitian at The Talbot Centre.

References

1. Yoong, S., Carey, M., Sanson-Fisher, R., & D’Este, C. (2012). A cross-sectional study assessing the self-reported weight loss strategies used by adult Australian general practice patients. BMC Family Practice, 13(1). doi: 10.1186/1471-2296-13-48
2. Quinn, D., Puhl, R., & Reinka, M. (2020). Trying again (and again): Weight cycling and depressive symptoms in U.S. adults. PLOS ONE, 15(9), e0239004. doi: 10.1371/journal.pone.0239004
3. Itsiopoulos, C., Brazionis, L., Kaimakamis, M., Cameron, M., Best, J., O’Dea, K., & Rowley, K. (2011). Can the Mediterranean diet lower HbA1c in type 2 diabetes? Results from a randomized cross-over study. Nutrition, Metabolism And Cardiovascular Diseases, 21(9), 740-747. doi: 10.1016/j.numecd.2010.03.005
4. Roizen, M. (2009). Adherence to Mediterranean diet and risk of developing diabetes: prospective cohort study. Yearbook Of Anesthesiology And Pain Management, 2009, 319-320. doi: 10.1016/s1073-5437(09)79195-8
5. Wenner, M, (2009), Does Inflammation Trigger Insulin Resistance and Diabetes? Scientific American, https://www.scientificamerican.com/article/inflammatory-clues/, accessed2021.
6. Zuhair S. Natto, Z., Yaghmoor, W., Alshaeri, H., Van Dyke, T (2019): Omega-3 Fatty Acids Effects on Inflammatory Biomarkers and Lipid Profiles among Diabetic and Cardiovascular Disease Patients: A Systematic Review and Meta-Analysis.Scientific Reports, 9, 18867.
7. Schwingshackl L, Hoffmann G: Mediterranean dietary pattern, inflammation and endothelial function: a systematic review and meta-analysis of intervention trials.(2014) Nutri Metabol Cardiovasc Dis NMCD, 24(9):929-939.
8. Haigh, L., Bremner, S., Houghton, D., Henderson, E., Avery, L., & Hardy, T. et al. (2019). Barriers and Facilitators to Mediterranean Diet Adoption by Patients With Nonalcoholic Fatty Liver Disease in Northern Europe. Clinical Gastroenterology And Hepatology, 17(7), 1364-1371.e3. doi: 10.1016/j.cgh.2018.10.044