The ‘food matrix’ describes a food in terms of both its structure and its nutrient content, and how these interact together. Foods consist of a large number of different nutrients that are contained in a complex physical structure. The nature of the physical structure together with the mix of nutrients and bioactives can impact nutrient digestion, absorption and metabolism, affecting the overall nutritional and health properties of the food1.
Nutrition research has traditionally focused on identifying the specific mechanisms and health impact of single nutrients – for example, saturated fatty acids in relation to blood lipids and cardiovascular disease (CVD). It has often then followed that nutrition policy is based on such associations - for example, recommendations to limit foods containing saturated fatty acids in order to reduce CVD risk.
More recently, however, nutrition research has shifted focus to examine the relationship of whole foods with health, including dairy foods. This is based on the premise that we do not eat nutrients in isolation but as foods, and meals, and part of dietary patterns. From this research, a different picture has emerged in some cases than might be predicted from the nutrient content of the foods investigated. Cheese is a good example: despite its saturated fat (and salt) content, the majority of epidemiological studies report that cheese consumption does not increase the risk of CVD and may, in fact, be beneficial2. Researchers have characterised this as a ‘food matrix’ effect1. This recognises that the health effects of a food are much more complex than that of a single nutrient it contains or even a few nutrients. Rather, they are a function of both a food’s structure and its nutrient composition, and how these interact with each other.
Milk and dairy products are complex foods containing numerous nutrients and bioactive components. The rich dairy matrix of nutrients includes protein, fat, lactose, calcium, phosphorus, potassium, vitamin B12, riboflavin (vitamin B2) and many other vitamins and minerals. Dairy is also rich in bioactive components - for example, small peptides with biological effects are produced when milk protein is digested in the intestine or during the fermentation process in foods such as cheese and yogurt3. Fermented dairy products also contain bacteria with the potential to produce beneficial short-chain fatty acids (SCFAs) in the gut4.
The nutritional and functional complexity in dairy food matrices is exemplified by milk fat, which has over 400 different fatty acids with different physiological properties3,5. Components of the membrane which encloses the fat droplets in milk (the milk fat globule membrane; MFGM) also have functional effects, for example in relation to lipid metabolism6.
The matrix of different dairy foods will differ in the amounts and combinations of nutrients, including proportions of whey and casein proteins, fat and bioactives. Within a dairy food category, production methods and processes will also alter the composition of the matrix - for example, the length of ripening time for cheese affects the extent of protein breakdown and production of bioactive peptides1.
In addition to their nutritional matrices, dairy foods also have complex physical matrices: from the solid matrix of cheese, gel-like structure of yogurt to liquid milk. Again, these differ within dairy categories - for instance, methods of production and ripening will influence the structure of the many different types of cheese.
The structure of a food matrix can have an impact on factors such as nutrient absorption and digestion and, therefore, the metabolic response after eating. For example, rates of gastric emptying can differ for liquid compared to solid or semi-solid structures and so affect satiety and appetite responses7. The matrix structure can also influence protein absorption and digestion, for example, between casein contained in the milk matrix and given as a supplement8.
Given the complex nature of dairy matrices, it is perhaps not surprising that there is increasing evidence that the health effects of dairy foods extend beyond their constituent parts. Beneficial matrix effects have been identified for cardiometabolic disease risk, body weight and bone health1.
For example, the effects of milk and dairy foods on bone health may be due in part to positive interactions of calcium, protein and phosphorus with each other and with lactose and bioactive peptides in the dairy matrices, rather than simply a ‘calcium effect’ as is often assumed. Similarly, the blood pressure lowering effect of milk may be the result of interactions between calcium, potassium, phosphorus and bioactive dairy peptides in the milk matrix.
In relation to cheese, the explanation for the potential beneficial rather than harmful effects on CVD may again lie in interactions of the components of the cheese matrix including calcium, phosphorus, the milk fat globule membrane and starter cultures, which modify saturated fatty acid-induced increases in blood lipids.
More research is underway to investigate the health effects of the dairy matrix and to unravel the mechanisms and pathways through which the different components work together. However, the matrix concept underlines the importance of considering the health effects of milk and dairy as whole foods, alongside the individual components they contain. This is particularly important in relation to public health policy, and there is a growing recognition that dietary guidance should be based on evaluation of the health impact of whole foods, including dairy, rather than on single nutrients.
1. Thorning TK et al. Whole dairy matrix or single nutrients in assessment of health effects: current evidence and knowledge gaps. Am J Clin Nutr 2017: 105:1–13. http://dx.doi.org/10.3945/ajcn.116.151548
2. Chen GC et al. Cheese consumption and risk of cardiovascular disease: a meta-analysis of prospective studies. Eur J Nutr. 2016 Aug 12; DOI: 10.1007/s00394-016-1292-z.
3. Muehlhoff et al. Milk and dairy products in human nutrition. Rome: Food and Agriculture Organisation of the United Nations; 2013. http://www.fao.org/docrep/018/i3396e/i3396e.pdf (accessed 01/12/13).
4. St-Onge MP et al. Consumption of fermented and nonfermented dairy products: effects on cholesterol concentrations and metabolism. Am J Clin Nutr. 2000; 71: 674–681.
5. Parodi PW. Milk fat in human nutrition. Aust J Dairy Technol. 2004; 59: 3-59.
6. Rosqvist F et al. Potential role of milk fat globule membrane in modulating plasma lipoproteins, gene expression, and cholesterol metabolism in humans: a randomized study. Am J Clin Nutr. 2015; 102: 20-30.
7. Tsuchiya A et al. Higher satiety ratings following yogurt consumption relative to fruit drink or dairy fruit drink. J Amer Diet Assoc. 2006; 106: 550-557.
8. Churchward-Venne TA et al. Ingestion of casein in a milk matrix modulates dietary protein digestion and absorption kinetics but does not modulate postprandial muscle protein synthesis in older men. J Nutr. 2015; 145: 1438-1445.