Blueberries

Blueberries

The blueberry (Vaccinium spp.; in Hebrew “אוכמניות”) is a small berry from the heath family (Ericaceae), and one of the most studied foods in the field of nutrition and cognition. Its deep blue-purple color comes from anthocyanins — pigments from the flavonoid family that are concentrated mainly in the skin, and around which almost all of the research revolves.

100 grams of blueberries provide about 57 calories, 14 grams of carbohydrates, 2.4 grams of fiber and about 120-160 mg of anthocyanins. It is a fruit relatively low in sugar (about 10 grams per 100 grams) with a low glycemic index (about 53), so it is well tolerated even in carbohydrate-restricted diets.

It is worth distinguishing between two types: cultivated blueberries (highbush, the common supermarket kind) and wild blueberries (lowbush/wild, sold mainly frozen). Wild blueberries are smaller, so their ratio of skin to volume is higher — and their anthocyanin content is about 50% higher or even more.

Research-based health benefits

• Cognition and memory — the most researched area: This is the blueberry’s unique research foundation. The Nurses’ Health Study, which followed tens of thousands of women for years, found that high intake of blueberries and strawberries was associated with a delay of up to about two and a half years in cognitive decline. Smaller controlled trials, in adults with mild cognitive decline and in children, showed improvements in memory and processing speed after consuming blueberries or blueberry extract. The proposed mechanism includes improved cerebral blood flow — demonstrated with fMRI — and effects on neuronal signaling pathways.

• Blood pressure and blood vessel function: Meta-analyses of controlled trials found a moderate drop in systolic blood pressure and improved endothelial function (FMD) with regular blueberry intake. The mechanism is similar to that of cocoa flavanols — increased nitric oxide availability and relaxation of the blood vessel wall.

• Insulin sensitivity: Several controlled trials in adults with insulin resistance showed improved insulin sensitivity after daily blueberry intake. The finding is consistent but modest in size.

• Fiber and the microbiome: 2.4 grams of fiber per 100 grams, combined with polyphenols, most of which are not absorbed in the small intestine and reach the colon. There they serve as a substrate for gut bacteria, which convert them into active metabolites — so a substantial part of the “antioxidant activity” actually takes place through the microbiome.

• Vitamin C and vitamin K: 100 grams provide about 9.7 mg of vitamin C and about 19 mcg of vitamin K.

• Low calorie density: 57 calories per 100 grams make them one of the “cheapest” fruits calorie-wise relative to their nutritional value — a practical advantage for weight management.

Important caveats

The “superfood” label attached to blueberries deserves some balance. Three caveats:

1. The ORAC score is irrelevant. For years blueberries were marketed on the basis of a high ORAC (oxygen radical absorbance capacity) score. The US Department of Agriculture (USDA) removed this database from its website in 2012, explicitly stating that ORAC values are measured in a test tube and have no proven biological meaning in the human body. Marketing based on ORAC is not valid.

2. The bioavailability of anthocyanins is low. Less than 1% of the anthocyanins consumed are absorbed intact into the blood. The effect is mostly mediated by metabolites formed in the gut — which also explains why the response varies between people.

3. The effect size is modest. The measured drops in blood pressure and cognitive improvements are real and statistically significant, but small. Blueberries are a good addition to the diet — not a therapeutic intervention.

Downsides and health considerations

• Price and availability: Fresh blueberries are significantly more expensive than most fruits, especially out of season. This is the most significant practical downside, and the solution is simple (see below on frozen).

• Vitamin K and anticoagulants: The content is moderate, but people taking warfarin (Coumadin) are advised to keep their intake of vitamin K-rich foods consistent and not to change it suddenly.

• Pesticides: Blueberries sometimes appear on lists of fruits with high residues. Since the value is concentrated in the skin and they cannot be peeled, thorough washing or choosing organic is relevant.

• FODMAPs in large portions: In small amounts blueberries are well tolerated on a low-FODMAP diet, but large portions may cause symptoms in sensitive people.

• Processed products: Blueberry muffins, jams and “blueberry-flavored” yogurts usually contain a lot of sugar and a negligible amount of fruit — and sometimes only flavoring and food coloring. The nutritional benefit does not survive the processing.

Nutrition facts per 100 grams

Frozen vs. fresh — a practical point

This is probably the most useful advice about blueberries. Frozen blueberries are not inferior to fresh ones, and are sometimes even better.

They are frozen using IQF (individually quick frozen) within hours of picking, at peak ripeness — whereas “fresh” blueberries sometimes go through weeks of transport and storage during which vitamin C and polyphenols degrade. Studies comparing the two found similar and even higher anthocyanin content in the frozen ones.

What’s more, ice crystals rupture the cell walls — which releases anthocyanins and may even increase their availability. Add the fact that frozen blueberries are significantly cheaper and available year-round (and are often wild blueberries rich in anthocyanins), and this is the better practical choice for most people.

To use: add frozen blueberries directly to a smoothie, yogurt or oatmeal. Slow thawing in the fridge preserves texture better than quick thawing.

Summary

Blueberries are a fruit with a genuine research base — mainly in cognition, where the evidence is unique compared to other fruits, and also in blood pressure and insulin sensitivity. The effect sizes are modest, and the ORAC score used to market them is not scientifically valid. They are an excellent addition to a varied diet, not a medicine. The most significant practical step: buy frozen — cheaper, available year-round, and at least nutritionally equivalent.