THE SHORT VERSION

  • In a 2014 breakfast experiment, 15 adults with well-controlled type 2 diabetes had lower blood glucose over three hours after whey than after water. Insulin and gut hormone responses were also higher.
  • Researchers are studying several possible explanations: insulin release, gut hormones, slower stomach emptying, and an enzyme called DPP-4. The breakfast trial did not establish DPP-4 blocking as the explanation.
  • Whey before a carbohydrate meal has lowered short-term blood glucose in several small studies of people with type 2 diabetes. These findings do not settle whether it improves glucose control over the long term.
  • The question to ask: has a comparable finished food or drink been tested, in whom, and over what period?

Fifteen adults with well-controlled type 2 diabetes took part in a breakfast experiment on two separate days. Before one breakfast, they drank 50 grams of whey mixed with water. Before the other, they drank water alone. The breakfast itself was the same on both days.1

Over the three hours after eating, blood glucose, or blood sugar, was lower after whey. Insulin and gut hormone responses were higher. Published by Jakubowicz and colleagues in 2014, the experiment helps explain why a protein has drawn interest in blood sugar research.1

The question starts with what happens around a meal. Protein digestion can change the signals that govern insulin release and how fast food leaves the stomach. Researchers are investigating how those responses shape the rise in blood glucose after eating.2

How protein can change the meal response

Blood glucose after a meal reflects several processes working together. These include how quickly the stomach passes food into the gut and how the body responds as nutrients are absorbed. Protein eaten before or with a meal can influence that sequence.2,3

Whey supplies amino acids that can stimulate the pancreas’s beta cells to release insulin. Researchers call this an insulinotropic effect, meaning that it stimulates insulin release.2

Insulin helps regulate glucose in the blood. A stronger early insulin response can therefore contribute to a smaller rise in blood glucose after a meal containing carbohydrate.2

Stimulating insulin release and improving insulin sensitivity are different processes. More insulin alongside lower glucose does not, by itself, show that the body’s tissues have become more responsive to insulin.

The gut contributes its own signals

Digestion also triggers the release of incretin hormones. These include glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Both help coordinate insulin release in response to nutrients. Researchers study how strongly these hormones act and how responsive the body is to them.2

GLP-1 came up in Part 9 in the context of fullness, but its role also includes glucose regulation. Appetite and blood glucose are separate outcomes. A change in one does not show a matching change in the other.

Gastric emptying, meaning how fast food leaves the stomach, is another part of the explanation. In a small 2009 study, Ma and colleagues tested eight people with diet-controlled type 2 diabetes on separate occasions.3

They compared whey consumed before a carbohydrate meal, whey added to the meal, and no whey. The serving given before the meal, called a preload, slowed stomach emptying and increased insulin and incretin responses.3

This helps explain why timing can matter. How quickly a protein is digested and how it affects the emptying of a later meal are related but separate questions.3

Why DPP-4 enters the story

Once released, incretin hormones do not stay active for long. An enzyme called dipeptidyl peptidase-4 (DPP-4) cuts and inactivates GLP-1 and GIP. Researchers ask whether certain food-derived peptides might block this enzyme and keep the hormones active for longer.4

Laboratory experiments have found DPP-4-blocking activity in digested milk proteins and in individual peptides. Both whey and casein have drawn interest as sources. These findings suggest possible explanations that still need testing in the body.4

An effect in a laboratory enzyme test leaves several steps unanswered. The peptide has to survive digestion, remain available, and reach the right site in an effective amount. To block DPP-4 in the bloodstream, it would also need to cross the gut lining.4

The 2014 breakfast trial gives a useful reality check. Whey increased GLP-1 responses and lowered glucose after the meal, but DPP-4 activity measured in the blood did not differ significantly between conditions.1

The result therefore did not establish DPP-4 blocking as the explanation for lower glucose.1

What the meal studies observed

MEASUREMENT OBSERVATION
Insulin response Higher after whey in the 2009 and 2014 trials.1,3
Gut hormones Higher GLP-1 responses in both trials; higher GIP responses in the 2009 trial.1,3
Stomach emptying Slower after the whey preload in the 2009 trial.3
Blood glucose Lower over three hours after 50 grams of whey before breakfast in the 2014 trial.1
DPP-4 activity No significant difference in blood DPP-4 activity in the 2014 trial. Blocking activity in laboratory peptide tests is a separate finding.1,4

These observations come from separate small trials in people with type 2 diabetes. They do not prove which pathway accounts for the lower glucose response.1,3

What a meal experiment can and cannot show

The breakfast study measured a response over a few hours in a small group with well-controlled type 2 diabetes. Comparing whey with water also meant that the whey condition supplied extra protein and calories. It did not compare whey with another protein providing the same calories.1

A smaller glucose response over a few hours does not establish diabetes prevention, lasting improvement in glucose control, or the same response in people with different metabolic health.

Looking beyond one meal

Longer studies help address a different question: whether the effect continues with repeated use. In a 12-week trial, 79 adults with type 2 diabetes were assigned to a drink containing 17 grams of whey plus guar fiber, or a placebo, before two meals a day.5

The whey-and-guar group had lower glucose after a test meal. At the end of the trial, its HbA1c was about 0.1 percentage point lower than the placebo group’s. HbA1c is a blood measure that reflects average glucose over the past few months.5

That was a small difference, and the drink combined whey with guar. The trial therefore cannot show what whey alone would do.5

A 2022 analysis pooling five trials of whey before meals also found lower glucose after eating. Its authors judged the certainty of the evidence insufficient and called for larger trials to assess the dose and longer-term effects.6

Reading the finding closely

These studies give researchers a physiological basis for investigating whey. They follow amino acid delivery, insulin release, gut hormone responses, stomach emptying, and peptide activity.1,2,3,4

How much each contributes can depend on the preparation, dose, meal, and people studied. The explanation for the glucose response and its lasting effects still need closer study.1,2,3,4

Related reading

References

Educational content. The Fountain is written to explain, not to make health claims about any product. This article summarizes published peer-reviewed research. Nothing here is medical advice.

  1. Jakubowicz D, Froy O, Ahrén B, et al. Incretin, insulinotropic and glucose-lowering effects of whey protein pre-load in type 2 diabetes: a randomised clinical trial. Diabetologia. 2014;57(9):1807–1811. https://doi.org/10.1007/s00125-014-3305-x
  2. Hidayat K, Du X, Shi BM. Milk in the prevention and management of type 2 diabetes: the potential role of milk proteins. Diabetes/Metabolism Research and Reviews. 2019;35(8):e3187. https://doi.org/10.1002/dmrr.3187
  3. Ma J, Stevens JE, Cukier K, et al. Effects of a protein preload on gastric emptying, glycemia, and gut hormones after a carbohydrate meal in diet-controlled type 2 diabetes. Diabetes Care. 2009;32(9):1600–1602. https://doi.org/10.2337/dc09-0723
  4. Caron J, Domenger D, Dhulster P, Ravallec R, Cudennec B. Protein digestion-derived peptides and the peripheral regulation of food intake. Frontiers in Endocrinology. 2017;8:85. https://doi.org/10.3389/fendo.2017.00085
  5. Watson LE, Phillips LK, Wu T, et al. A whey/guar “preload” improves postprandial glycaemia and glycated haemoglobin levels in type 2 diabetes: a 12-week, single-blind, randomized, placebo-controlled trial. Diabetes, Obesity and Metabolism. 2019;21(4):930–938. https://doi.org/10.1111/dom.13604
  6. Chiang SW, Liu HW, Loh EW, et al. Whey protein supplementation improves postprandial glycemia in persons with type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials. Nutrition Research. 2022;104:44–54. https://doi.org/10.1016/j.nutres.2022.04.002