The new data, published in the Journal of Nutritional Biochemistry, reports that ingesting fats similar to those in a Mediterranean-type diet, featuring low saturated fat and high monounsaturated fat, appears to decrease the inflammatory response, both in comparison to a high saturated fat diet, as well as in relation to a low-fat diet.
The team, led by Professor C. Lawrence Kien at the University of Vermont, also noted that enhanced inflammatory responses could be the key link between high saturated fat intake - a recognised risk factor for obesity-related disorders - and the development of diseases like type 2 diabetes and atherosclerosis.
"It has been recognized that obesity - a disorder characterized by abnormally high accumulation of fats in the body - and an unhealthy diet can increase the risk of chronic metabolic diseases such as atherosclerosis, type 2 diabetes, and Alzheimer's disease, but not in everyone," said Kien.
Inflammation, obesity & disease risk
Inflammation is a normal part of the immune system's defence against infection. However some environmental, internal, and dietary compounds can stimulate inflammatory responses, causing side effects that also occur during infections – which can have longer-term health consequences.
Indeed, Kien and his team noted that research showing saturated fat generally has metabolic effects via indirect mechanisms, and the fact that metabolic diseases have an inflammatory component, led them to test the theory that the pro-inflammatory effect of saturated fat might be facilitating how they impact the risk of metabolic disease.
"Scientists have strived to understand the effects of dietary fats on inflammation by studying isolated cells and animal model systems," said Kien – who noted that a 2011 study reported that palmitic acid, the most prevalent saturated fat in the diet, increased the production of the inflammatory cytokine, interleukin-1beta (IL-1beta) via a process involving activation of an innate immune system response called the NLRP3 inflammasome.
However, the question remained whether these findings were relevant to human diets, he said.
In the new study, the team studied healthy, lean and obese adults, enrolled in a randomised, cross-over trial comparing three-week diets, separated by one-week periods of a low fat diet.
One experimental diet was similar to the subjects' habitual diet and was high in palmitic acid; the other experimental diet was very low in palmitic acid and high in oleic acid, the most prevalent monounsaturated fat in the diet. After each diet, a number of outcomes were measured, including those related to inflammation.
Kien and his team reported that relative to the low palmitic acid diet, the high palmitic acid diet stimulated the production of cytokines modulated by the NLRP3 inflammasome, thus creating more inflammation and associated risk for metabolic disease.
They said the findings demonstrate for the first time that varying the normal range of palmitic acid found in common human diets influences the production of IL-1beta.
"In other words, habitual diet and especially the type of fat ingested may determine, in part, the risks associated with obesity,” said Kien.
"Ultimately, we would like to understand how these dietary fats behave - both shortly after ingestion, as well as when stored in adipose tissue as a consequence of many months of ingestion - and thus contribute to inflammation and the risk of metabolic disease," he explained – adding that it is important to acknowledge that other factors like physical activity ‘and other features of complex diets’ will determine how persistent, high intake of saturated fat will impact health.
Source: Journal of Nutritional Biochemistry
Published online ahead of print, doi: 10.1016/j.jnutbio.2015.07.014
"Lipidomic evidence that lowering the typical dietary palmitate to oleate ratio in humans decreases the leukocyte production of proinflammatory cytokines and muscle expression of redox-sensitive genes"
Authors: C. Lawrence Kien, et al