Reducing dairy consumption may improve metabolic syndrome, study finds

18 Nov 2020 --- A lower dairy intake may be beneficial for people with metabolic syndrome, according to a new trial published by researchers from the Fred Hutchinson Cancer Research Center in Seattle, US.

“Unlike previous observational studies, which suggested a beneficial relationship between fermented dairy foods – such as yogurt, as well as high-fat dairy foods – and better metabolic health, our rigorous randomized, controlled trial could not confirm that eating more dairy foods lowers people’s blood sugar levels,” says Dr. Mario Kratz, an associate professor in Fred Hutch’s Public Health Sciences Division.

Prior studies had shown that consumption of at least two servings of dairy per day has been linked to lower risks of diabetes and high blood pressure, as well as the cluster of factors that heighten cardiovascular disease risk and metabolic syndrome.

Regulating blood sugar levels
The study, published in the American Journal of Clinical Nutrition, received funding from several dairy organizations, including the US National Dairy Council and the Dairy Farmers of Canada. The researchers examined dairy’s impact on regulating blood sugar levels in people with metabolic syndrome.

The findings showed that the body’s ability to regulate blood sugar levels was not directly affected by whether participants consumed dairy foods. However, consumption of either low-fat or full-fat milk, yogurt and cheese reduced insulin sensitivity.

The study showed that the body’s ability to regulate blood sugar levels was not affected by the intake of dairy.The project was inspired by previous observational studies suggesting people who ate the most yogurt or full-fat dairy foods tended to have a lower risk of Type 2 diabetes. 

“More work needs to be done examining the impact of diets rich in dairy in healthy populations,” Kratz notes. 

“However, the findings of reduced insulin sensitivity that resulted from higher dairy intake may be concerning for people with metabolic syndrome and similar conditions such as prediabetes or Type 2 diabetes,” he explains.

Risk factors for metabolic syndrome
Metabolic syndrome is a group of risk factors that raises the risk of heart disease, diabetes, stroke and other health problems. 

Insulin sensitivity refers to how the body’s cells respond to insulin. High insulin sensitivity allows the body cells to use blood sugar more effectively, reducing blood sugar.

The study involved 72 volunteer men and women who had metabolic syndrome. Using a parallel-design, randomized, controlled trial, the research team randomized the volunteers into three groups over 12 weeks:

• A limited dairy diet, consisting of no dairy foods other than – at most – three servings of skim milk per week.
• A low-fat dairy diet, consisting of more than three servings of skim milk, non-fat yogurt and low-fat cheese per day.
• A full-fat dairy diet, consisting of more than three servings of whole milk, full-fat yogurt and full-fat cheese per day.

After the 12 weeks, Kratz and his research team measured various biomarkers, including blood sugar throughout a glucose tolerance test, systemic inflammation and liver-fat content. 

They found that blood sugar regulation was not directly affected by whether participants consumed dairy foods. 

The consumption of either low-fat or full-fat milk, yogurt and cheese reduced insulin sensitivity, the research notes.However, participants on the full-fat dairy diet gained a modest amount of weight. Participants on both low-fat and full-fat dairy diets saw a decrease in insulin sensitivity. 

A reduction in insulin sensitivity could lead to an increased risk of Type 2 diabetes in the long term, the researchers conclude.

However, because dairy foods were not affected by blood sugar levels, the long-term impact of reduced insulin sensitivity in people eating a diet rich in dairy on Type 2 diabetes risk is unclear.

Further research warranted
Kratz also feels strongly that a single study should always be interpreted with caution. 

First, dairy-rich diets had not reduced insulin sensitivity in all previous trials. Second, it is important to consider that even though the dairy-rich diets reduced insulin sensitivity, this did not lead to higher blood sugar levels in these participants, he says.

Because blood sugar is the clinical endpoint the research team cared more about – and was the primary endpoint in this trial – these results’ interpretation is not straightforward. 

Lastly, when evaluating the overall health effects of a food group such as dairy, the researchers propose that food’s impact on the regulation of blood sugar levels is just one of many considerations.

Edited by Kristiana Lalou