Switching to a 10-day Mediterranean-style diet improves mood and cardiovascular function in a controlled crossover study

The Mediterranean diet (MedDi) has become a very popular dietary recommendation for the prevention of chronic diseases. Being characterized by a high consumption of fresh vegetables, fruits, whole grains, nuts, and legumes, moderate consumption of fatty fish, olive oil, and dairy products, and low consumption of red meat and poultry, it is not surprising to see why. Previous research has shown, quite literally, that the MedDi food choices are associated with the greatest protection from diet-induced chronic diseases. Dairy, nuts, and fish are especially beneficial for health.

There is also some evidence that a MedDi is beneficial for cognitive health. Observational research has suggested that adherence to a MedDi slows global cognitive decline in otherwise healthy older individuals. Other research has suggested memory benefits are attributable to the antioxidant-rich food choices. Even in younger individuals, consumption of a MedDi for a mere ten days resulted in significant improvements in self-rated vigor, alertness, and contentment, although changes in cognitive performance variables were less conclusive with the MedDi condition being associated with faster spatial working memory, but with slower numeric working memory and word recognition.

The overall cognitive changes are interesting, especially since they came about in such a short period of time. As such researchers from Australia sought to replicate them with a more stringent randomized crossover design. Using 24 young and healthy women, mood, cognition, and cardiovascular function were assessed before and after switching from a usual diet to a MedDi for ten days.

“Participants were provided with an eating plan when undertaking the MedDi condition and daily food diaries to record their food intake over the course of the study. The requirements of the MedDi included increasing consumption of fruits, vegetables, oily fish, low-fat dairy, and nuts over the 10-d period, focusing on foods that provided a source of carbohydrates, protein, and healthy fats. When possible, participants were instructed to ensure all foods were freshly prepared, and to exclude all pre-prepared, packaged, and processed foods. Participants were instructed to abstain from consuming meat, butter and margarine, caffeinated/energy drinks, added sugars and salts, alcohol, and the use of tobacco or illicit drugs throughout the diet-change period. In the normal diet condition, participants were instructed to continue their diet as per usual, but still document their eating habits in the food diary.”

Compliance to the MedDi was excellent, and there was even an unintentional weight loss of 1.77 kg in the MedDi groups compared to no weight change in the normal diet. Similar to the previous findings, a MedDi led to a significant reduction in confusion and significant increase in alertness and contentment. Word recall also improved, suggesting improved memory, but working memory suffered. Finally, there was a minor improvement in cardiovascular health via improved augmentation index.

Bottom line

We have no idea what the women in the study were eating or what their macronutrient ratios were on either diet. Nonetheless, assuming the standard Western diet and acknowledging the average 94% compliance to the MedDi, the mood and cardiovascular improvements are somewhat impressive for being such a short period of time. Again, the cognitive outcomes are mixed, but they may take more time to manifest… as would other markers of cardiovascular health for that matter. Cholesterol, for example, takes at least two weeks to change significantly. The weight loss was also surprising and I have a hunch that it was lost water weight from a reduction of intestinal inflammation that is so common with a standard Western diet.

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