*Geek Box: Categorising Dairy Foods
Within the sum of the food group known overall as “dairy” is a complex diversity in individual foods, that differ relative to their form and processing. The broad use of the term “dairy” in fact only describes the common origin of the foods, and does not necessarily reflect the various levels at which dairy foods may be differentiated: fermented vs. unfermented; refined vs. unrefined; whole-milk [“full-fat”] vs. non-fat/low-fat; solid vs. liquid.
And these alterations are not academic, but relate to differential effects of the food products on intermediate risk factors, e.g., blood cholesterol levels, that in turn may provide biological plausibility to the associations between specific dairy foods and cardio-metabolic health outcome. So, let’s discuss the categorisations by which we can differentiate dairy foods.
Fermented dairy produce includes fermented milks (e.g., kefir, buttermilk), yogurts, and cheeses. Fermentation has historically provided a means of preservation, and the process of fermentation yields particular nutritional characteristics, including provision of lactic acid bacteria, higher protein content (in the case of certain yogurts), and formation of bioactive peptides which may exert beneficial effects on blood lipids, pressure, gut immune and microbiota function.
Whole milk may also be subject to various refinement processes. For example, butter is produced by separating cream from whole milk, and churning the cream until the fat separates from the remaining liquid, a process which alters the nutritional composition. This distinction is thus made by categorising the food as refined [i.e., butter] or unrefined [i.e., cheese].
The refinement process alters the nutritional characteristics of the end product. Compared to cheese, butter is low in calcium, higher in fat, and the process of churning removes the milk fat globule membrane [MFGM], a tri-layered membrane rich in bioactive phospholipids and proteins which encloses the milk fat.
A final distinction can be made between whole-milk produce vs. non-fat or low-fat produce, the definitions of which related to the milk fat content: whole-milk contains 3.5% fat on average, semi-skimmed milk 2.5%, and skimmed milk 0.1% fat. The differences in fat content are achieved by mechanically separating the fat from the liquid milk.