Could eating whey protein before meals help reduce blood sugar spikes?

From full-fat milk to probiotic yogurt and whey protein, researchers examine whether what we consume, how it is prepared, and when we eat it could influence blood sugar regulation.

The Role of Milk and Dairy Products in Type 2 Diabetes and Prediabetes: A Narrative Review of Randomized Trials. Image Credit: Madeleine Steinbach / Shutterstock

In a recent narrative review published in the journal Nutrients, the researchers synthesized evidence from 57 randomized controlled trials (RCTs) to examine the effects of milk and dairy products on glycemic control in adults with type 2 diabetes mellitus (T2DM) and prediabetes.

The included trials examined acute and chronic interventions to determine how differences in dairy composition, fat content, and proteins could influence human glucose metabolism.

The researchers found that while increasing overall dairy consumption produced heterogeneous and largely neutral effects on long-term glycated hemoglobin (HbA1c), targeted strategies (e.g., structured whey protein preloads) more consistently reduced short-term postprandial glycemic excursions (post-meal blood sugar spikes), potentially through effects on incretin hormones, insulin regulation, and gastric emptying.

Background

Type 2 diabetes mellitus (T2DM) and prediabetes are major metabolic health challenges associated with impaired glucose regulation and an increased risk of cardiovascular complications.

Decades of research have established that these conditions are physiologically driven by insulin resistance (impaired cellular responsiveness to insulin) and progressive pancreatic beta-cell (β-cell) dysfunction, prompting traditional dietary guidelines to recommend that patients restrict their intake of saturated fats (associated with increased cardiovascular risks).

Yet the scientific community remains divided over the physiological impacts (metabolic roles) of dairy products. The 2025–2030 Dietary Guidelines for Americans recommend daily consumption of full-fat dairy without added sugars, but clinical literature offers conflicting evidence on whether dairy fats and proteins protect against or worsen metabolic deterioration.

Reviews of past trials are necessary, as individual investigations have assessed different dairy products, formulations, and outcomes, making comparisons difficult and leaving uncertainty about the roles of fermentation, fortification, and isolated dairy proteins.

About the review

This review aimed to clarify the evidence and inform future medical nutrition therapy by narratively synthesizing randomized controlled trials (RCTs) indexed in PubMed through April 7, 2026. The authors did not strictly follow the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines but used a PRISMA-style flow diagram to describe the selection process. The study identified 246 records, screened 176 after removing duplicates, and included 57 studies: 46 on T2DM and 11 on prediabetes.

The review grouped interventions by dairy type, including fluid milk with different fat contents, fermented products such as yogurt and kefir, fortified dairy products enriched with nutrients or prebiotics, and isolated dairy proteins, particularly whey and casein.

The researchers assessed fasting plasma glucose (FPG), HbA1c, fructosamine, measures of insulin resistance, including HOMA-IR, and postprandial incretins, including glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) concentrations.

Review findings

Across the trials, chronic dairy intake showed no uniform glycemic benefits, with outcomes heavily governed by specific product formulations. Included RCTs indicate that increasing low-fat or high-fat dairy intake to 3 or more daily servings did not significantly change participants’ HbA1c, fasting glucose, or HOMA-IR indices compared with consuming habitual diets. A separate trial involving overweight adults, including some with prediabetes, found greater insulin resistance with a predominantly low-fat, high-dairy diet than with a red-meat-based diet, particularly among women.

In one 12-week trial involving 48 adults with T2DM, a high-energy breakfast enriched with whey reduced HbA1c by 0.89 percentage points, outperforming breakfasts rich in other proteins or carbohydrates. Other trials found no additional HbA1c benefit from adding whey to exercise programs. Selected fortified and fermented formulations, such as vitamin D- and calcium-fortified yogurt drinks, improved some glycemic and insulin sensitivity measures, though effects varied across studies and may reflect the added nutrients rather than dairy itself.

Prediabetes trials found that yogurt containing heat-treated Lactiplantibacillus plantarum (OLL2712) modestly reduced participants’ HbA1c at 12 weeks compared with conventional yogurt, but the difference was no longer significant eight weeks after treatment stopped. In a separate small study, a milk protein hydrolysate preload was associated with HbA1c returning below the prediabetes threshold in just over half of 21 participants after six weeks without establishing lasting remission.

Preload trial outcomes suggested that ingesting 15 to 50 grams of whey protein before meals can improve short-term postprandial regulation, though an optimal dose and timing have not been established. In one trial involving 15 adults with T2DM, a 50-gram whey preload taken 30 minutes before breakfast reduced overall post-meal glucose exposure by 28% and increased insulin and intact GLP-1 responses compared with water. Higher insulin or incretin concentrations did not always translate into better glucose control.

Finally, one acute trial involving 22 men with T2DM found that combining a whey preload with the dipeptidyl peptidase-4 (DPP-4) inhibitor vildagliptin improved post-meal glucose regulation more than either intervention alone, encouraging further research on the topic.

Conclusions

The findings suggest that dairy products cannot be regarded as a monolithic entity, as their metabolic impacts are influenced by the specific product’s matrix structure, processing, dose, fortification, and consumption timing.

While generalized dairy increases fail to guarantee glycemic improvements, structured whey protein preloads and selected yogurt formulations containing bacterial preparations may be inexpensive, accessible additions to existing diabetes care, rather than substitutes for established dietary and medical treatment. Their longer-term benefits and effects on β-cell function remain uncertain.

The authors acknowledge that most existing chronic intervention trials remain limited by short durations (predominantly 4 to 24 weeks) and small cohort sizes, calling for future research to incorporate larger, longer, sex-balanced trials and real-world assessments to confirm long-term benefits and adherence and further investigate interactions between whey preloads and modern glucagon-like peptide-1 receptor agonists (GLP-1 RAs). Such combinations could improve glucose regulation but might also worsen gastrointestinal symptoms.

Source:

Journal reference:

- Kolbe, P., Kietaibl, A. T., & Rega-Kaun, G. (2026). The Role of Milk and Dairy Products in Type 2 Diabetes and Prediabetes: A Narrative Review of Randomized Trials. Nutrients, 18(20), 3407. DOI: 10.3390/nu18203407. https://www.mdpi.com/2072-6643/18/20/3407