Strawberries - Healthy Benefits Through Antioxidants
The commercially available garden strawberries (Latin: Fragaria × ananassa) belong to the rose family and are classified under the subfamily Rosoideae. The garden strawberry originated in the 18th century from a crossbreeding of two wild strawberry varieties from Chile and North America.
Especially during the season (end of May to early August), strawberries should be incorporated into a healthy diet.
Strawberries are among the best sources of bioactive compounds 1 2 3. Bioactive compounds have health-promoting benefits on living organisms. The content and composition of these compounds depend on the variety, location, environmental conditions, growth conditions, ripening stage, harvest time, as well as subsequent storage conditions or processing methods 4 5 6.
Some scientists classify strawberries as a functional food with various preventive and therapeutic benefits 7.
Are Strawberries Nuts?
By the way, strawberries are not technically berries, but aggregate fruits. Strawberries are the only fruits that carry their seeds, also known as achenes, on the outside (about 200 per strawberry). The small achenes are the actual fruits, and the red strawberry itself is a false fruit.
A large portion of strawberries, approximately 91%, consists of water. Due to their low fat content of 0.3g per 100g and high water content, they contain very few calories, about 32kcal per 100g. The majority of calories come from the amounts of fructose (2.4g) and glucose (2g). Overall, strawberries contain 7.7g of carbohydrates. Due to their low calorie content, strawberries can also be helpful for weight loss.
Healthy dietary fiber is also present in strawberries, with 2g per 100g. Dietary fiber itself cannot be digested by the body. However, it is needed for a healthy digestive tract as it serves as a food source for intestinal bacteria.
Adequate intake of dietary fiber can be beneficial in preventing obesity, type 2 diabetes, hemorrhoids, gastroesophageal reflux disease (abnormal acid reflux into the esophagus), duodenal ulcers, colorectal cancer, diverticulitis (protrusions in the intestinal wall), gastrointestinal disorders, constipation, stroke, hypertension, as well as cardiovascular diseases 8 9.
With the consumption of strawberry powder for 3 weeks, risk factors for cardiovascular diseases, stroke, and diabetes were reduced in obese patients. 10. Scientists suggest strawberries as a food to reduce obesity-related diseases.
Strawberries are among the fruits richest in vitamin C, with 58.8 mg per 100 g. They contain more vitamin C than lemons in the same quantity. With a cup of fresh strawberries, about 150% of the daily requirement for vitamin C can be met. Vitamin C is important for the immune system, skin health, and the production of hormones and neurotransmitters, thanks to its antioxidant benefits. 11.
Minerals in Strawberries
Reactive oxygen species and free radicals are responsible for accelerated aging and increased occurrence of diseases such as inflammation, arthritis, immune system impairments, various types of cancer, and heart diseases 12. The compounds in strawberries can act preventively against the mentioned diseases 13 14 15.
In comparison to other fruits such as raspberries, oranges, and plums, strawberries exhibit greater antioxidant activities 16. Strawberries contain high levels of antioxidant phytochemicals 17 18. These primarily include vitamin C, carotenoids, and polyphenols 19 20. Polyphenols, classified as secondary metabolites, are aromatic compounds. In total, 40 phenolic compounds have been described in measurements 21. Among them are the bioactive compounds found in strawberries: flavonoids (such as anthocyanins), flavonols (such as quercetin, kaempferol, myricetin, cyanidin), ellagic acid, catechins, tannins (such as ellagitannins), and phenolic acids (such as hydroxybenzoic acids and hydroxycinnamic acids) 22 23.
- Antioxidant benefit (neutralizes free radicals)
- Antimicrobial and anti-inflammatory benefits
- Antihypertensive (blood pressure-lowering) properties
- Modulate gene expression, which plays an important role in cell metabolism and cell survival
- Protect and repair DNA
For example, fresh strawberry juice has high antioxidant activity against peroxyl radicals, superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen 30.
Studies have shown that daily consumption of strawberries leads to a moderate but scientifically significant increase in antioxidant capacity in healthy individuals 31 32. Female study participants consumed 250g of frozen strawberries daily for a period of three weeks. Antioxidant capacity expresses the ability of a food to capture and neutralize free radicals and oxygen radicals.
Strawberries are among the most important foods in the United States in terms of consumption, offering protection against oxidative damage with an antioxidant content of 2.139 mmol per 100 g (ranked 27th). They could potentially provide a shield against oxidative damage. 33. The top three spots are occupied by ground cloves (125.549 mmol, all per 100 g), dried oregano leaves (40.299 mmol), and ground ginger (21.571 mmol) 34.
Furthermore, strawberries also reduce oxidative damage to low-density lipoproteins (LDL) and lower blood lipid levels 35.
Other scientists conclude from their in vitro study with human gastric epithelial cells that strawberry tannins stimulate digestion in the stomach and exert anti-inflammatory benefits 36.
Moreover, the small achenes also contribute to the antioxidant capacity of the pseudofruit 37. They also contain bioactive compounds.
Strawberries for Heart Health
Consumption of strawberries with high levels of flavanones, anthocyanins, and flavonoids is associated with a reduced risk of mortality (caused by coronary heart disease and cardiovascular diseases) in postmenopausal women 38.
Especially with prolonged consumption of strawberries, the number of chronic inflammations can be reduced and plasma fat levels improved. 39 40. This primarily supports cardiovascular health, especially in individuals at higher risk for metabolic syndrome. 41. Metabolic syndrome encompasses cardiovascular risk factors such as high blood pressure, dyslipidemia, and increased waist circumference.
According to a study, consuming 3 cups of strawberries per day for eight weeks resulted in a reduction of bad LDL cholesterol (from 3.5 to 3.1 mmol/L) in 27 overweight men and women with metabolic syndrome. 42. Additionally, the average cholesterol level was reduced by 9% (from 5.8 to 5.2 mmol/L). This benefit is likely due to the antioxidant properties of anthocyanins. Elevated LDL cholesterol levels are associated with an increased risk of strokes and heart attacks. The results also indicate that strawberries improved atherosclerotic risk factors such as dyslipidemia and circulating adhesion molecules in patients with metabolic syndrome.
In a 2013 study involving 93,600 women, consuming strawberries and blueberries, which are also rich in anthocyanins, was associated with a 34% lower risk of heart attack. 43.
The predominant anthocyanin is pelargonidin-3-O-glucoside at 61%, followed by cyanidin-3-O-glucoside in strawberry extracts 44. During digestion, a portion of the anthocyanins is lost. However, pelargonidin-3-glucoside remains the most abundant anthocyanin with nearly 12 mg per 100 g of digested strawberries 45. Apparently, the timing of strawberry consumption is also important. Drinking a strawberry beverage two hours before breakfast resulted in higher levels of pelargonidin in the plasma compared to during or two hours after the meal 46. The anthocyanin pelargonidin gives strawberries their red color.
Breeders are working on developing new cultivars of strawberries with higher anthocyanin content than previously available strawberries. 47.
Protection of Red Blood Cells
According to studies, strawberries could also have an anti-hemolytic effect on erythrocytes. 48. Hemolysis refers to the dissolution of red blood cells (erythrocytes). In a 16-day study involving 12 healthy subjects who consumed 500g of strawberries daily, an increase in serum vitamin C concentrations and plasma antioxidant capacity was observed. Vitamin C is a crucial antioxidant that neutralizes free radicals and reactive oxygen species, thereby preventing cellular damage. Consequently, vitamin C exhibits high antioxidant activity. 49.
Another study shows that with a 2-week consumption, a significantly improved resistance to oxidative hemolysis in red blood cells could be achieved 50.
Strawberries Beneficial for the Skin
Strawberry extracts contain polyphenol compounds that can protect human cells and the skin from the harmful effects of UV-A radiation 51. The extracts exhibited photoprotective activity in fibroblasts (movable cells in connective tissue), increased cell viability, and reduced DNA damage. UV-A rays are suspected to cause skin cancer.
In addition, strawberries, with their antioxidant properties, provide a way to protect the skin from oxidative stress and aging 52.
Fighting Cancer with Strawberries
Strawberries also contain a plant compound called fisetin, which has neurotrophic (acts on nerves), anticarcinogenic, anti-inflammatory, and other health-promoting benefits 53. Fisetin is also an antioxidant belonging to the group of flavonoids.
Studies on prostate and lung cancer cells have shown that fisetin inhibits two chemical pathways (PI3K/Akt and mTOR) 54. These pathways are usually overactive in tumors. Dual inhibitors of the PI3K/Akt and mTOR signaling pathways are considered valuable agents for cancer treatment. Scientists hope that compounds like fisetin could offer a new therapeutic option for cancer treatment.
Strawberry extracts have been studied for their ability to inhibit the growth of oral, breast, colon, and prostate cancer cell lines 55 56 57. The extracts counteracted cell proliferation (rapid tissue growth and multiplication). They also exhibited pro-apoptotic (cell-suicide inducing) benefits against colorectal cancer cell lines. Extracts significantly inhibited cell proliferation in liver cancer cells as well 58.
In another study, extracts were found to have anti-cancer activities on cervical and breast cancer cell lines 59.
Other findings indicate that freeze-dried strawberry powder (60 g per day) has the potential to prevent esophageal cancer 60.
Delay Cognitive Decline with Strawberries
In addition, strawberries have potential relevance to neurological health 61.
Increased consumption of strawberries and blueberries can slow down cognitive decline in older adults 62. The results suggest that cognitive aging can be delayed by 2.5 years.
Diabetes and Blood Sugar Control
Strawberries are a very good source of polyphenols 63. These can help with blood sugar control and reduced fat storage.
In addition, strawberries have a low glycemic index of 40 and a low glycemic load of 1 64. This indicates that they do not cause significant spikes in blood sugar. When blood sugar levels rise, the body releases the hormone insulin, which signals the cells to absorb glucose from the blood for energy metabolism or to store it as glycogen.
Other study findings suggest that ellagitannins and ellagic acid have good potential for managing hyperglycemia (high blood sugar) and hypertension (high blood pressure) associated with type 2 diabetes 65.
By consuming 50g of freeze-dried strawberries daily (equivalent to approximately 500g of fresh strawberries) for 6 weeks, improved glycemic control and a better antioxidant status were achieved in patients with type 2 diabetes. 66. Furthermore, lipid peroxidation (free radicals attacking lipids) and the number of inflammatory reactions were reduced. The scientists recommend strawberries as an adjunct therapy for alleviating metabolic complications in patients with type 2 diabetes.
Additional results also show benefits on inflammatory responses and insulin sensitivity due to antioxidants. 67. Consuming strawberry beverages with a carbohydrate-rich meal can reduce the body's insulin response more than consuming a placebo beverage.
Other studies with obese adults also suggest 68. In the 12-week study, the benefits of strawberries on selected biomarkers (parameters for measuring biological processes) related to antioxidant status in obese adults with elevated serum lipids were measured. Strawberries increased antioxidant capacity in plasma, glutathione levels (important antioxidant), and catalase enzyme activity. With increased catalase enzyme activity, more hydrogen peroxide (oxidizing agent) is catalyzed into water and oxygen. Overall, according to scientists, strawberries can provide additional protection against obesity-related conditions such as cardiovascular diseases, metabolic syndrome, and type 2 diabetes.
Ultimately, strawberries are suitable as a healthy food for diabetics.
Strawberries are highly perishable and should be processed quickly. These healthy fruits are great raw in salads, yogurts, cereals, and smoothies. Cakes and pies with strawberries are also very popular.
Strawberries can be processed into jam, ice cream, juices, jellies, and compotes, among other things. They are also used in punches. When frozen, they can be sucked on. However, freezing destroys the thin skin, so they don't look as appetizing after thawing as they do fresh. Additionally, the water in strawberries expands during freezing, making them mushy after thawing. Nevertheless, this doesn't affect the taste.
They taste sweetest at room temperature. Strawberries should be stored in a cool place. For example, the healthy polyphenols last longer at 4 °C 69.
Processing methods such as heating, pressing, and pasteurization cause strawberries to lose a large portion of their healthy phenolic compounds 70.