Benefits
After-meal blood sugar and insulin with a high-carbohydrate breakfast
In a crossover trial funded by the National Processed Raspberry Council, 21 adults with excess weight, prediabetes and insulin resistance ate the same carbohydrate-rich breakfast with 0, 125 or 250 g of frozen raspberries. Both amounts lowered the 2-hour insulin response versus no berries, and 250 g also lowered peak and 2-hour glucose. In 36 older adults, 25 g of powder with a meal cut peak glucose by 8% versus the meal alone.
Inflammation markers after a meal and over 4 weeks
In a randomized crossover study in obese adults with type 2 diabetes, IL-6 and TNF-alpha were lower 4 hours after a breakfast with raspberries than after the same meal alone, and were also lower after 4 weeks of daily raspberries than after 4 weeks without them; CRP did not change. An 8-week trial of 280 g a day and a single-meal trial in adults with prediabetes found no change in these markers.
Endothelial function after drinks made with red raspberries
In a double-blind crossover trial in 10 healthy men, drinks providing 200 g or 400 g of red raspberries improved flow-mediated dilation, a measure of how well an artery widens, at 2 and 24 hours versus a matched control drink. The larger amount did no better. Pooled trials found no significant change in blood pressure or blood lipids. Funding included the National Processed Raspberry Council.
Eight weeks of daily frozen raspberries in adults with excess weight
In an 8-week randomized trial in 59 adults with overweight or abdominal obesity, 280 g a day of frozen raspberries did not change insulin, glucose, inflammation markers or blood pressure compared with keeping a usual diet. Blood gene activity and some blood metabolites shifted in the raspberry group. The Washington Red Raspberry Commission funded the trial.
Raspberries eaten with starchy foods
In a crossover test in 12 volunteers, pancakes with 100 g of raspberries gave the same blood glucose response as control pancakes matched for fruit sugars. In a Finnish meal study in healthy women, 150 g of raspberry puree with white bread was not among the berries that significantly lowered the insulin response. Both tests were in people without known blood sugar problems.
Gut bacteria shifts during 4 weeks of daily raspberries
In a 4-week crossover trial in 26 adults with prediabetes and insulin resistance, the equivalent of 125 g of fresh red raspberries a day raised Eubacterium eligens and lowered Ruminococcus gnavus from baseline, and total and LDL cholesterol fell from baseline. Both periods included raspberries, so there was no berry-free comparison. The National Processed Raspberry Council helped fund it.
Source of ellagitannins, anthocyanins, fiber and vitamin C
The USDA lists 52 kcal, 6.5 g of fiber and 26.2 mg of vitamin C per 100 g of raw raspberries. Lab analysis of red raspberries found the ellagitannin sanguiin H-6 in significant amounts, less lambertianin C, and eleven anthocyanins based on cyanidin and pelargonidin. This is a composition note, not a measured health effect.
Mechanism of action
Ellagitannins are turned into urolithins by gut bacteria
After people ate 300 g of raspberries, no intact ellagitannins appeared in urine; instead, urolithin A and B conjugates appeared 7 to 48 hours later, but not in people without a colon (ileostomy), and the profile varied widely between individuals. In a vascular trial, plasma ellagic acid and urolithin A conjugates tracked the improvements in artery widening.
Anthocyanins are poorly absorbed intact
Raspberry anthocyanins appeared in urine at under 0.1% of intake. In people with an ileostomy, 40% of the anthocyanins and 23% of sanguiin H-6 reached the end of the small intestine, so much of the berry's polyphenol load passes on to the colon, where bacteria break it down.
Ellagitannin fractions relax blood vessels in lab tests
When red raspberry extract was split into fractions in the lab, vessel-relaxing activity was found only in fractions holding lambertianin C and sanguiin H-6, and sanguiin H-6, vitamin C and the anthocyanins accounted for most of the antioxidant capacity. These are laboratory findings, not effects measured in people.
Clinical trials
Randomized, controlled, three-arm, single-blinded crossover trial: the same high-carbohydrate, moderate-fat breakfast with 0 g (control), 125 g or 250 g of frozen red raspberries on three separate days, with blood sampled for 8 hours and again at 24 hours; funded by the National Processed Raspberry Council. (Xiao et al. 2019, Obesity (Silver Spring))
32 adults: 21 with overweight or obesity, prediabetes and insulin resistance, and 11 metabolically healthy reference adults.
In the prediabetes group, both 125 g and 250 g lowered the 2-hour insulin area under the curve versus control, and 250 g also lowered peak insulin, peak glucose and the 2-hour glucose area under the curve (P < 0.05). After-meal blood fats did not differ from control. Markers of oxidative stress and immune signaling did not differ between meals. Single meals only.
Randomized crossover study with no masking: an acute phase of a high-fat breakfast with or without raspberries (250 g of frozen red raspberries in the trial registry) on 2 days at least 1 week apart, then a 10-week phase of 4 weeks with and 4 weeks without daily raspberries, separated by a 2-week washout; the registry lists Oklahoma State University as lead sponsor. (Schell et al. 2019, Ann Nutr Metab)
Obese adults with type 2 diabetes; a ClinicalTrials.gov record by the same investigator (NCT03403582), which matches the meal phase but is not linked in the PubMed record, lists 25 enrolled.
Serum glucose was lower at 2 and 4 hours after the raspberry meal than after the control meal, and IL-6 and hsTNF-alpha were lower at 4 hours (all p < 0.05). After 4 weeks, IL-6 and hsTNF-alpha remained lower than in the control phase. Fasting glucose, fasting blood fats, CRP and the elasticity of the blood vessels did not change; after-meal blood fats at 4 hours and, after 4 weeks, systolic pressure showed only downward trends.
Randomized, single-blinded, controlled crossover study of a high-carbohydrate, moderate-fat meal with 0 g (control) or 25 g of freeze-dried red raspberry powder, with blood sampled over 7.5 hours and memory tests before and after the meal; the abstract does not state the funding source. (Xiao et al. 2026, Br J Nutr)
36 adults aged 55 to 70 (mean 61) with overweight or obesity (mean BMI 30.0); 19 women and 17 men.
The raspberry meal lowered peak glucose by 8%, insulin at 30 minutes and the overall insulin response compared with control (P < 0.05). After the raspberry meal, participants made fewer attempts on a paired-associates learning task and fewer errors on a spatial working memory task (P < 0.05); the abstract does not present these as differences from the control meal. Blood vessel function did not differ.
Three-arm, double-blind, randomized, controlled crossover trial of drinks providing 200 g or 400 g of red raspberries (201 or 403 mg of total polyphenols) or a matched control drink, with flow-mediated dilation measured at baseline, 2 hours and 24 hours; funders included the National Processed Raspberry Council. (Istas et al. 2018, Arch Biochem Biophys)
10 healthy men.
Flow-mediated dilation improved versus control at 2 hours (by 1.6% with 200 g and 1.2% with 400 g) and at 24 hours (1.0% and 0.7%). The larger amount did not give a larger effect. Plasma ellagic acid and urolithin A conjugates correlated with the improvements. A short study in 10 healthy men.
Two-arm, parallel-group, randomized controlled trial of 280 g a day of frozen raspberries versus keeping the usual diet for 8 weeks; funded by the Washington Red Raspberry Commission. (Franck et al. 2020, Nutrients)
59 adults with overweight or abdominal obesity and slightly raised fasting hormone or blood fat levels.
The between-group comparisons showed no significant change in the main outcomes, which covered body measurements, fasting hormone and sugar levels, immune markers and pressure readings. In the raspberry group, 43 blood genes changed activity and 10 serum metabolites shifted, including beta-alanine and trimethylamine N-oxide. The authors judged the supplementation to have no meaningful effects on these outcomes. No adverse events related to raspberries were reported.
Crossover meal test: pancakes with 50 g of raspberries in the batter and 50 g on the side, pancakes with blueberries, or control pancakes matched for fruit sugars, plus a reference food; no specific grant funded the study. (Clegg et al. 2011, Br J Nutr)
12 volunteers (3 men, 9 women; mean age 33) without diabetes.
The raspberry pancakes gave the same rise in sugar in the blood as the matched control pancakes, and the area under the response curve and a fullness index also did not differ. The authors concluded that the idea that berries blunt the response to starchy foods is unsubstantiated.