Blackberries: one trial, and it used 600 g a day

Blackberries have one real trial behind them, and it used a dose almost nobody eats. Twenty-seven overweight men ate 600 g of blackberries a day for a week. At the 5.3 g of fibre per 100 g in the table below, 600 g works out at roughly 32 g of fibre a day from the berries alone. That is a research dose, and nobody is putting it forward as a portion. Against a matched control their insulin response fell by about a fifth, from an area under the curve of 8245 down to 6485, and they burned slightly more fat. The glucose curve itself did not move. That is seven days, in men only, at a dose you are unlikely to repeat. Most of the rest on this page was measured on something other than the fruit. The 27.4 percent drop in blood sugar further down this page came out of a different study, in 16 healthy volunteers who ate bread, so it does not contradict the flat glucose curve above. What those volunteers were given was a mixture of green tea, strawberry, blackcurrant and blackberry, and the share belonging to the berry was never measured. The oxidative stress study used 400 mL of juice. The one on how older bodies handle anthocyanins used a test meal carrying cocoa and citrus flavonoids alongside the blackberry. What comes from the food itself is the plain number on the label. Raw blackberries carry 5.3 g of fibre and 15.4 mg of vitamin C per 100 g.

The numbers, per 100 g

What your body absorbs

• A mixture of green tea, strawberry, blackcurrant and blackberry cut the blood glucose rise from bread by 27.4% at the lower dose and by 49.0% at the higher one in 16 healthy volunteers, and the share belonging to blackberry was never measured. — 16 healthy volunteers, randomised single-blind crossover, bread as the carbohydrate load, testing a four-part polyphenol and fibre mixture rather than blackberry on its own (n = 16) Evidence B source
  Glucose incremental AUC -27.4% (sd 7.5) at the single dose and -49.0% (sd 15.3) at the double dose, insulin AUC -46.9% (sd 13.4), with alpha-amylase inhibition shown in vitro for blackberry among other components

What cooking and storage change

• Listeria monocytogenes grew on the whole unbroken surface of blackberries at 22 and 35 degrees Celsius, as it did on the intact surface of every other produce item tested except carrot. — 10 whole intact raw produce commodities including blackberry, inoculated with a five-strain cocktail and held at 2, 12, 22, 30 and 35 degrees for up to 28 days (n = 6 samples per condition) Evidence D source
  Growth on the intact surface of every commodity except carrot, with all 10 supporting growth at 22 and 35 degrees; behaviour at 2 and 12 degrees varied by commodity

What it does to your health

• Eating 600 g of blackberries a day for a week shifted 27 overweight men toward burning fat and cut their insulin response by about a fifth against a matched control. — 27 overweight or obese men on an investigator controlled high-fat diet, randomised crossover, 7 days per period (n = 27) Evidence B source
  24 h respiratory quotient 0.810 against 0.817 (p = 0.040), insulin AUC 6485 against 8245 microunit x min per mL (p = 0.0002), HOMA-IR improved (p = 0.0318), glucose AUC unchanged
• Among 29 217 US adults surveyed over 14 years, people who reported eating blackberries had 37% lower odds of sleep difficulty, and no other berry showed that link. — 29 217 US adults aged 20 and over, NHANES 2005 to 2018, two 24 h dietary recalls (n = 29217) Evidence C source
  Adjusted odds ratio 0.63 (95% CI 0.40 to 0.97, p = 0.036) for sleep difficulty among blackberry consumers; berry consumers overall had 10 to 17% lower risk of short sleep

Safety, limits and interactions

• In an 18-case hepatitis A outbreak across five Canadian provinces, blackberries came up with an odds ratio of 7.21, and the investigators still could not confirm any source. — 18 cases of hepatitis A virus infection with three matched controls each, five Canadian provinces, onsets October 2017 to May 2018 (n = 18 cases) Evidence C source
  Shrimp or prawns OR 15.75 (p = 0.01) and blackberries OR 7.21 (p = 0.02) as foods of interest, with no confirmed outbreak source

Who this works differently for

• After a meal with 390 mg of blackberry anthocyanins, 163 adults recovered a similar total amount of flavonoid metabolites in urine, but older people reached peak excretion later in 92% of the cases where age mattered. — 163 healthy UK adults aged 18 to 30 or 65 to 77, single-arm intervention with 24 h urine collection (n = 163) Evidence C source
  No group difference in total 24 h recovery; 20 of 76 metabolites differed in time to peak excretion by age and 9 by sex, with later peaks in older participants in 92% of instances

What is still unknown

• A 400 mL bolus of juice rich in blackberry anthocyanins and vitamin C left markers of oxidative stress unchanged in 12 healthy non-smokers. — 12 healthy non-smokers, randomised controlled crossover, single 400 mL dose against a sugar solution (n = 12) Evidence B source
  Plasma ascorbic acid rose and total oxidant scavenging capacity was maintained, while isoprostane and DNA strand breaks did not improve and rose after both drinks

The bottom line

Keep them cold. Listeria monocytogenes grew on the whole unbroken surface of blackberries at 22 and 35 degrees Celsius in a laboratory test, which is a reason to keep the punnet in the fridge rather than on the counter. That study inoculated the fruit on purpose and counted bacteria rather than illness, so take it as a reason to refrigerate and not as a reason to worry. Canning costs you most of what makes them worth eating. Per 100 g, blackberries canned in heavy syrup carry 19.7 g of sugar against 6.5 g raw, 2.8 mg of vitamin C against 15.4 mg, and 3.4 g of fibre against 5.3 g. Frozen unsweetened keeps the fibre at 5.0 g and still loses the vitamin C, down to 3.1 mg. If you want the vitamin C, the fresh punnet is the only version that delivers it. You will see blackberries linked to sleep. Among 29 217 US adults surveyed over 14 years, people who reported eating them had 37 percent lower odds of sleep difficulty, and no other berry showed the same link. That is a cross-sectional survey resting on two days of recalled food and self-reported sleep, the blackberry eaters inside it are a small group, and nothing in it tells you which came first. Buying blackberries to sleep better is not something this supports. Now the part we cannot fill. We hold no upper limit for blackberries, and we found no work at all on how they interact with medicines. Our corpus holds zero records on blackberries in pregnancy and zero on blackberries in children. The section that on other pages says who should be careful is empty here, and leaving it silent would let you read absence as an all-clear. The one safety signal we did find stayed unresolved. In an 18-case hepatitis A outbreak across five Canadian provinces, blackberries came up with an odds ratio of 7.21, and the investigators never confirmed a source. Eighteen cases, food recalled over months, no conclusion. It is a loose end, and refrigerating your fruit and washing it is the whole of what anyone can honestly tell you to do about it.

Sources

1. bbry-r3-02 · randomised controlled trial
   Plasma glucose was lower after consumption of both doses compared with controls: lower dose, change in mean incremental areas under the glucose curves (IAUC)=-27·4 (sd 7·5) %, P<0·001; higher dose, IAUC=-49·0 (sd 15·3) %, P<0·001
   Br J Nutr, 2016 · checked 2026-09-23
2. bbry-r3-07 · laboratory food microbiology study
   L. monocytogenes was able to grow on the whole intact surface of all produce tested, except for carrot. The 10 produce commodities supported growth of L. monocytogenes at 22 and 35°C.
   J Food Prot, 2021 · checked 2026-09-23
3. bbry-r3-01 · randomised controlled trial
   The BB treatment resulted in a significant reduction in average 24 h respiratory quotient (RQ) (0.810 vs. 0.817, BB vs. GEL, p = 0.040), indicating increased fat oxidation...However, the insulin AUC was significantly lower with the BB compared to the GEL control (6485 vs. 8245 µU·min/mL, p = 0.0002), and HOMA-IR improved with BB (p = 0.0318).
   Nutrients, 2018 · checked 2026-09-23
4. bbry-r3-05 · cross-sectional survey analysis
   A decreased risk of sleep difficulties was found to be linked to blackberry consumption (adjusted OR = 0.63, 95% CI: 0.40-0.97; p = 0.036) but not for other berries.
   Nutrients, 2023 · checked 2026-09-23
5. bbry-r3-06 · case-control study
   Results of the analysis pointed to shrimp/prawns (odds ratio (OR) 15.75, p = 0.01) and blackberries (OR 7.21, p = 0.02) as foods of interest, however, an outbreak source could not be confirmed.
   Epidemiol Infect, 2019 · checked 2026-09-23
6. bbry-r3-03 · clinical intervention study
   Healthy males and females (n = 163) prospectively recruited on the basis of age (18-30 y or 65-77 y) and sex consumed a standardized flavonoid-rich test meal providing 640-mg cocoa/chocolate flavan-3-ols, 340-mg citrus flavanones, and 390-mg blackberry anthocyanins...Of 76 metabolites, 20 had significantly different times of maximum urine excretion (Tmax) by age and 9 by sex, with a later mean Tmax observed for older participants (92% of instances).
   Am J Clin Nutr, 2025 · checked 2026-09-23
7. bbry-r3-04 · randomised controlled trial
   Within a randomized controlled crossover trial, 12 healthy nonsmokers ingested 400 mL of a blended juice of these fruits or a sugar solution (control)...This anthocyanin-rich fruit juice may stabilize the pro-/antioxidant balance in healthy nonsmokers without affecting markers of oxidative stress.
   J Agric Food Chem, 2012 · checked 2026-09-23