With the rising costs of health care and pharmacological interventions, the role of natural dietary measures in the prevention and treatment of cardiovascular diseases has gained special attention. To our knowledge this is the first study investigating the effects of freeze-dried strawberry powder supplementation on selected cardiovascular risk factors in women with metabolic syndrome. Serum cholesterol levels were lowered following four weeks of freeze-dried strawberry consumption, which suggests a need for further study to determine if this might be a potential dietary approach to lowering cholesterol levels in obese women. In our study, subjects consumed a daily dose of 50 g freeze-dried strawberry powder which is equivalent to approximately 500 g fresh strawberries (3.5 cups). Our study findings add to the scientific basis supporting the cardio protective role of fruits and vegetables in human diet [7, 19]. Some of the known cardio protective agents in strawberries include phytochemicals, vitamin C, folic acid, potassium, fiber and phytosterols, contributing to the antioxidant, anti-inflammatory, and hypocholesterolemic effects of strawberries [1, 15, 20].
To our knowledge, the effects of strawberry consumption on features of metabolic syndrome, oxidative stress, and inflammation have not been investigated in obese adults. Jenkins et al. have previously reported the cardiovascular health benefits of strawberries . In their study, 28 hyperlipidemic subjects with an average baseline total and LDL-cholesterol of 5.62 ± 0.14 mmol/L and 3.61 ± 0.13 mmol/L, respectively, did not show any significant differences in lipid levels following intake of 454 g fresh strawberries everyday for four weeks. However, the study showed a significant reduction in thiobarbituric acid-reactive substances in LDL, indicating reduced oxidative damage to lipids. It should be noted that subjects in their study were following a cholesterol-lowering diet including soy, viscous fiber, plant sterols, and nuts for a mean of 2.5 years prior to strawberry supplementation for 4 weeks. Thus, the antioxidant effects of strawberries could have been confounded by the various dietary modifications made by these subjects . In our study, subjects had a lower baseline total and LDL-cholesterol levels (5.32 ± 0.2 mmol/L and 3.2 ± 0.17 mmol/L, respectively) compared to the reported data by Jenkins et al. which indicates that freeze-dried strawberry powder supplementation may reduce cholesterol in subjects with mild elevation than those with high cholesterol levels. Cholesterol-lowering effects of freeze-dried strawberry powder may be attributable to the phytosterol, fiber, or phytochemical content of strawberries. Phytosterols have been shown to inhibit cholesterol absorption and lower cholesterol levels in clinical studies [22, 23]. Since plant foods are natural sources of phytosterols, supplementation of concentrated fruit powder may be a novel approach to lowering selected CVD risk factors in women with clinically significant obesity (BMI >35), as noted in our study. Furthermore, the total dietary fiber content of the strawberry drink (8 g/day) may also contribute to the cholesterol lowering effects. The decreasing trend in oxidized-LDL in our study bears consideration and further research. Because oxidized-LDL plays a critical role in the initiation and progression of atherosclerosis , long-term supplementation of antioxidant-rich fruits, like strawberries may be beneficial in slowing or reversing the process of atherosclerotic cardiovascular disease in obese women with metabolic risk factors.
Our study findings of a significant decrease in MDA & HNE support similar effects reported by Pajk et al. in a porcine model of oxidative stress following supplementation of a fruit mixture including strawberries . Thus, further study is warranted to examine whether free radical damage can be significantly decreased by dietary intervention with freeze-dried strawberry powder. Due to the lack of a control group and the small sample size comprising only women, our study results cannot be widely generalized. But, the high compliance rate, bioavailability of strawberry ellagic acid, and tolerability of the freeze-dried strawberry drink, suggests that larger, controlled interventions using strawberry supplementation are feasible. Furthermore, since none of our subjects were on lipid-lowering medications, and no significant dietary changes were noted before and after supplementation, our data indicate that the improvements in lipids and lipid peroxidation may possibly be due to strawberry powder supplementation per se. Sub-analyses of the dietary data, among daily users of dietary supplements, did not show any significant differences at 4 weeks on variables of interests, suggesting that diet and supplementation did not confound our study findings. However, such effects need to be confirmed in well-controlled clinical trials.
Data from the National Health and Nutrition Examination Survey (2001-2002), reveal that US adults consume 53.5% whole fruit recommendations, mainly as apples, pears and bananas, while vegetable intake is significantly below the recommendations by the Dietary Guidelines for Americans, 2005. Fruit servings include grain-based desserts and fruit juices which are popular food items, but constitute a high-fat and high-sugar means of consuming fruits . Thus, to increase the intake of antioxidant-rich fruits and vegetables in the diet, concentrated fruit powders blended as smoothies may be a more attractive and convenient approach, especially for adults who do not consume the recommended amounts of fruits and vegetables. Our data suggest the need for a randomized controlled trial including a well-defined population of adequate sample size in assessing the effects of freeze-dried berry powder, as antioxidants and anti-inflammatory agents in adults with obesity and related metabolic disorders.