Mediterranean diet with a dairy twist shows promise in lowering heart disease risk

A recent Nutrients journal study evaluated how the combination of Mediterranean diet (MedDiet) supplement and dairy foods affected the gut microbiome in Australians at a high risk of cardiovascular disease (CVD).

Study: Interactions between Mediterranean Diet Supplemented with Dairy Foods and the Gut Microbiota Influence Cardiovascular Health in an Australian Population. Image Credit: DiViArt / Shutterstock

Background

Diet plays an essential role in regulating immunity and maintaining metabolic health. Improper diet is often linked to the development of obesity, cardiovascular diseases, and type 2 diabetes. Long-term adherence to a specific dietary pattern aids in shaping the intestinal commensal microbiota. The gut microbes produce several bioactive compounds by metabolizing dietary components, influencing host metabolic and immune homeostasis. 

Gut microbes produce short-chain fatty acids (SCFAs), such as acetate, butyrate, and propionate, through the fermentation of non-digestible fiber. These SCFAs are the primary sources of energy for colonic tissues to modulate inflammatory pathways, maintain gastrointestinal tissue integrity, and inhibit the proliferation of pathogenic bacteria. Alteration of specific gut bacteria lowers triglyceride levels, reduces systemic inflammatory markers (e.g., C-reactive protein), and improves liver function. 

All gut microbial products are not beneficial to humans. For instance, microbial metabolism of L-carnitine and choline results in the production of trimethylamine N-oxide (TMAO), which is a metabolite associated with the manifestation of atherosclerosis and inflammation. Both L-carnitine and choline are commonly found in nuts, dairy, meat, fish, and eggs.

MedDiet contains fruits, vegetables, nuts, extra virgin olive oil (EVOO), legumes, and cereals. This diet type recommends the consumption of moderate amounts of fish, dairy foods, eggs, poultry, and red wine. Furthermore, MedDiet is associated with low consumption of red meat, processed food, and discretionary foods (e.g., cakes and sweets). 

An abundance of bioactive nutrients, such as fiber, polyphenols, vitamins and minerals, antioxidants, and monounsaturated fats, has been associated with MedDiet, which promotes beneficial effects through the gut microbiota. Long-term adherence to the MedDiet significantly improves obesity, metabolic syndrome, diabetes, and dyslipidemia. 

It must be noted that a typical MedDiet provides calcium much below the Australian recommended daily intake (RDI). Calcium plays an important role in the formation and maintenance of bone, vascular dilation and contraction, cell differentiation, neuronal activity, and cell signaling for muscle function. Insufficient calcium intake leads to reduced bone strength and enhances pregnancy complications. It also enhances the risk of CVDs. The MedDiet supplemented with dairy products, such as milk, yogurt, and cheese, would fulfill Australian calcium intake recommendations. It is essential that a MedDiet fulfills all nutritional requirements before recommendation.

About the Study

The current randomized controlled trial (RCT) followed a 2 × 2 cross-over design to compare the benefits of MedDiet supplemented with dairy food (MedDairy) and low-fat (LFD) diet (control) in Australians at high risk of CVD. 

This study recruited adults between the ages of 45 and 75 years. All participants had high systolic blood pressure (SBP) but were not under any medication. Individuals who consumed medicinal levels of calcium or omega-3 supplements daily were excluded.

Participants were randomly assigned to any one of the groups, i.e., MedDairy (Group 1) or LFD (Group 2), and dietary interventions continued for 8 weeks, separated by an 8-week washout phase where participants followed their habitual diet. Complete fecal and clinical samples were collected at baseline and at 8 weeks to assess both groups.

Study Findings

At baseline, there were no significant differences between the study groups. Group 1 contained 18 participants, and group 2 contained 16 participants. All participants who were not following MedDiet at baseline exhibited increased MedDiet adherence through the MedDairy intervention. Along with the MedDiet, participants received 3 to 4 servings of any one of the dairy products, such as low-fat Greek yogurt, low-fat milk, cheese (hard, soft, semi-soft), and tzatziki dip.

Fecal microbiota analysis indicated no significant difference in the overall structure and composition of the fecal microbiota between the two study groups. However, a modest decrease in microbial diversity was observed in the LFD group. It must be noted that the MedDairy diet did not result in a significant change in the gut microbiota but considerably altered the abundance of selected bacterial taxa, such as Butyricicoccus, Lachnospiraceae, and Streptococcus, and a reduction in Colinsella and Veillonella.

Conclusions

The findings of the current study highlighted that 8 weeks of a Mediterranean diet supplemented with dairy foods resulted in changes in the relative abundance of certain bacterial taxa. MedDairy diet enhanced Butyricicoccus , which has a positive effect on systolic blood pressure. Therefore, adherence to the MedDairy diet could reduce CVD risks.