Whey before meals may blunt blood sugar spikes, but dairy effects vary

A review of 57 randomised trials suggests dairy has no single effect on glucose control, with product type, processing and timing shaping the outcome.

Researchers are increasingly finding that dairy may not affect blood sugar in a single, straightforward way. A narrative review in the journal Nutrients, based on 57 randomised controlled trials, suggests that the impact of milk, yoghurt, whey and other dairy products on glucose control depends heavily on what form the food takes, how it is processed and when it is eaten.

The review looked at adults with type 2 diabetes and prediabetes, drawing on trials of both short-term and longer-term interventions. According to the authors, broad increases in dairy intake did not produce consistent improvements in glycated haemoglobin, or HbA1c, the marker that reflects average blood sugar over roughly three months. But more targeted approaches, particularly whey protein taken before meals, appeared to curb post-meal glucose rises more reliably.

That finding fits with earlier evidence. A separate umbrella review indexed on PubMed, which brought together 13 systematic reviews and meta-analyses, found that whey protein may reduce HbA1c, insulin resistance and fasting insulin in people who are overweight or at risk of metabolic syndrome, although evidence was weaker in lower-risk groups. Another systematic review and meta-analysis concluded that whey protein improves post-meal blood sugar in people with type 2 diabetes, likely by increasing insulin secretion, boosting incretin hormones, slowing gastric emptying and affecting appetite.

The Nutrients review also pointed to important differences between products. Some fortified or fermented dairy items, including yoghurt drinks enriched with vitamin D and calcium, improved certain measures of glucose handling and insulin sensitivity, although the authors cautioned that the benefit may have come from the added nutrients rather than dairy itself. In one prediabetes study, yoghurt containing the bacterial strain Lactiplantibacillus plantarum OLL2712 modestly lowered HbA1c during treatment, but the effect faded after the intervention ended.

Whey protein preloads were among the most striking examples. In one trial, 50 grams taken 30 minutes before breakfast reduced post-meal glucose exposure by 28% in adults with type 2 diabetes and increased insulin and GLP-1 responses, a hormone linked to blood sugar regulation. Yet the review found no settled answer on the best dose or timing, and it noted that higher insulin or incretin levels did not always translate into better glucose control. The authors said the overall lesson is that dairy should not be treated as one uniform food group, but as a set of products whose effects vary with composition, processing and timing. They also stressed that most trials have been small and short, leaving longer-term benefits, adherence and interactions with newer diabetes drugs still uncertain.