There is a great deal of interest how cocoa flavanols (a type of antioxidant ) like monomers and procyanidins might prevent obesity and type-2 diabetes, though little is actually known how they might work. 

A new study compared the impacts of long-term dietary exposure to cocoa flavanol monomers, oligomers and polymers on the effects of high-fat feeding. Mice were fed a high-fat diet supplemented with either a cocoa flavanol extract or a flavanol fraction enriched with monomeric, oligomeric, or polymeric procyanidins for 12 weeks. 

The oligomer-rich fraction proved to be most effective in preventing weight gain, fat mass, impaired glucose tolerance, and insulin resistance in this model. This is the first long-term feeding study to examine the relative activities of cocoa constituents on diet-induced obesity and insulin resistance.

Flavanols in other foods, such as grapes and tea, are said to help fight weight gain and type-2 diabetes, but not all flavanols are created equal. Cocoa has several different kinds of these compounds, so researchers in the new study decided to tease them apart and test each individually for health benefits.

The mice were fed different diets, including high-fat and low-fat diets, and high-fat diets supplemented with different kinds of flavanols. 

Credit: DOI: 10.1021/jf500333y

They found that adding one particular set of these compounds, known as oligomeric procyanidins (PCs), to the food made the biggest difference in keeping the mice's weight down if they were on high-fat diets.

They also improved glucose tolerance, which could potentially help prevent type-2 diabetes.

"Oligomeric PCs appear to possess the greatest antiobesity and antidiabetic bioactivities of the flavanols in cocoa, particularly at the low doses employed for the present study," the researchers state.

Citation: Melanie R. Dorenkott, Laura E. Griffin, Katheryn M. Goodrich, Katherine A. Thompson-Witrick, Gabrielle Fundaro, Liyun Ye, Joseph R. Stevens, Mostafa Ali, Sean F. O’Keefe, Matthew W. Hulver, and Andrew P. Neilson, 'Oligomeric Cocoa Procyanidins Possess Enhanced Bioactivity Compared to Monomeric and Polymeric Cocoa Procyanidins for Preventing the Development of Obesity, Insulin Resistance, and Impaired Glucose Tolerance during High-Fat Feeding', J. Agric. Food Chem., 2014, 62 (10), pp 2216–2227 February 24, 2014 DOI: 10.1021/jf500333y