The Mediterranean diet—high in nuts, olive oil, and vegetables with a moderately reduced but varied consumption of fish, meat, and dairy—has gained notoriety as an ideal diet for human health. Populations in regions from which the diet draws its name are protected against a variety of diseases, including diabetes and cardiovascular and metabolic diseases. The imparted health benefits are believed to be attributable to a variety of compounds in the diet’s plant-based components known as polyphenols. Recent work published in BMC Medicine has found that polyphenols likely contribute to the health benefits provided by the Mediterranean diet, and further enrichment of these compounds in the traditional Mediterranean diets reduces unhealthy visceral fat.
Visceral fat, the bad one
Not all fat is created equal. Fat depots in the body are characterized by their location and function. Subcutaneous fat, lying just below the skin, is considered to be relatively inert; however, visceral fat, located deep within the abdominal cavity, has been associated with an increased risk of cancer, cardiovascular disease, and type 2 diabetes.
Even in individuals at a healthy weight, dyslipidemia—a condition marked by disproportionally large amounts of visceral fat—can result in increased systemic inflammation through the secretion of hormones known as adipokines. This “hidden” fat, popularly referred to as TOFI (thin outside, fat inside), has complicated the use of percent body fat and body mass index (BMI) as reliable metrics for health.
Polyphenols are a loosely categorized and diverse group of chemicals containing a phenol ring and commonly found in plants. Their consumption has for many years been associated with positive health outcomes. It is thought that this group of chemicals provides both antioxidant and anti-inflammatory benefits, aiding in the prevention of cardiovascular disease, type 2 diabetes, and hypertension; however, the effects of polyphenol consumption on obesity are not well known.
The traditional Mediterranean diet, containing a relatively high amount of plant food sources, is rich in polyphenols and has been shown to enhance the reduction of visceral fat when paired with moderate exercise. Recent trials have set out to determine if a further increase of polyphenols alone is sufficient in reducing the amount of visceral fat.
The 18-month Dietary Intervention Randomized Control Polyphenols Unprocessed (DIRECT-PLUS) trial examined the effects of a modified Mediterranean diet containing fewer red and processed meats and more polyphenols (green-MED diet). In order to attain high levels of polyphenols, the green-MED diet was supplemented with green tea and mankai duckweed (Wolffia globose), two plants rich in polyphenols and thought to provide health-related benefits.
When compared to both a diet formulated along healthy dietary guidelines and a traditional Mediterranean diet, the green-Med diet showed an improvement in adiposity through the reduction of visceral fat depots. Although both styles of Mediterranean diet provided some form of weight loss, the green-Med diet showed a reduction in visceral fat twice that of the traditional Mediterranean diet. In accordance with the reduction of visceral fat, the green-Med diet improved the profile of circulating lipids, improving both triglyceride and cholesterol levels.
Another fat depot found deep within the abdominal cavity, deep subcutaneous adipose tissue, was found to be equally reduced. This fat is structurally similar to the subcutaneous fat found beneath the skin but, much like visceral fat, the accumulation of this fat is associated with impaired glucose metabolism. The reduction of deep subcutaneous fat in the subjects fed a green-MED diet was, as expected, associated with improved markers of glucose metabolism.
Findings such as these support ever-growing evidence that achieving a healthy diet and healthy amounts of body fat are more nuanced than simply accounting for calories or body fat percentage. Food sources, especially plants, contain chemicals that seem to act directly on metabolic pathways similarly to the actions of pharmaceuticals. Understanding and utilizing dietary components such as phytochemicals can contribute to a dietary regimen optimized for human health.