The study, hosted by Massey University’s Riddet Institute working alongside the University of Otago’s Department of Human Nutrition and industry partner NIG Nutritionals (NIGN), recently received a grant of $1,410,978 by High-Value Nutrition (HVN) Ko Ngā Kai Whai Painga National Science Challenge.
The work will look at three different types of milk powder: goat milk, provided by NIGN; cow milk, provided by Māori dairy company Miraka; and sheep milk, provided by Spring Sheep Milk Co.
Riddet Institute professor of nutritional sciences Warren McNabb said the study will be the first trial of its kind and will involve four groups of about 30 volunteer participants aged 60 and older.
McNabb said the nutrient requirements of the elderly made this age group a good one to focus upon.
He said the 60-plus age group is a growing one in Asia and New Zealand, so it was considered ideal in terms of future commercial applications for any of the study’s findings.
“Milk is a good source of protein. Metabolically this age group doesn’t digest protein well, and milk is easy to digest,” McNabb said.
The study, which will take place over about 14 weeks, will build on earlier Riddet Institute research that indicates milk from different species have differing composition and milk structural assemblies, such as casein micelles, which could lead to differences in nutrition and digestive comfort.
“We know from the work we’ve done that compositionally they are different, and that the structural assemblies in the milks are different,” he said.
He said scientists have also established that the acid reaction in the stomach results in differences to at least casein and whey gastric digestion between goat, sheep and bovine milks.
“In the human stomach we know that cow’s milk forms a casein ‘curd’ that tends to be harder than it is with goat and sheep’s milk gastric curds,” he said.
This means the rate the digestive system can process the milk curds and get them from the stomach to the small intestine to be further digested and absorbed is likely to differ with the different species’ milks.
He said the hypothesis is that blood amino acids will rise at different rates, connected to the hardness of the casein curd forming in the stomach and how quickly it breaks down. Bovine milk is the hardest, closely followed by goat’s milk. The casein curds from sheep milk are much softer.
“We think the rise in amino acids in the blood will have different shapes,” she said.
“The anecdotal evidence is that goat and cow milk composition is roughly the same. But sheep’s milk is very different, with a higher protein and lipid content.”
Along with the differences with nutrient absorption, the study aims to identify the impact on digestive comfort, nutritional status and skeletal muscle function from adding whole milk powders to the diets of older adults.
He said it is not about determining which milk is good, bad, or better, but discovering useful nutritional evidence that can help consumers decide between products, depending on what they want to achieve. The different milks may be found to be more suitable for different nutritional needs, such as those of an athlete and the elderly, for instance.
He said there is potential for future studies to target other age groups, but plant-based milks are currently not being considered for inclusion as they are not viewed as a good source of nutrition.
Clinical trials will be hosted by the University of Otago, with participants consuming 250ml of milk twice-a-day and filling in questionnaires to record experiences of gut comfort, along with a control group that does not consume the milk. Blood glucose testing, blood pressure and faecal sampling will also be undertaken.
“We will get a really good handle of the effects of older adults drinking milk in terms of their nutritional status, blood glucose, gut comfort, vitality, how they sleep, sort of thing,” he said.
“We will also be able to figure out, are there differences between the milks?”
The study hopes to be recruiting participants by the middle of the year. It should be completed by Christmas.
Its findings will be published in scientific journals and widely publicised through media releases to news media, as well as being available on the Riddet Institute website and via social media.