New research finds that minimally processed blueberry protein bars can deliver (poly)phenols just as effectively as raw blueberries, challenging the notion that only fresh fruits offer full nutritional benefits. Study: Bioavailability and pharmacokinetics of (poly)phenols following consumption of selected blueberries and a blueberry-rich protein bar by adult males and females: a randomized, crossover, controlled trial. Image Credit: Bukhta Yurii / Shutterstock A randomized controlled trial conducted at North Carolina State University reveals that food processing minimally affects the bioavailability of (poly)phenols abundantly present in raw blueberries and blueberry-enriched protein bars. The findings are published in the American Journal of Clinical Nutrition. Background Fruits and vegetables rich in phytochemicals are known to offer several health benefits, including the prevention of non-communicable diseases. Despite these health benefits, less than 13% of Americans meet the daily recommended dietary intake. Low fruit and vegetable consumption can be associated with socioeconomic and cultural factors, and more specifically, customer choices driven by taste, price, and convenience. The commercialization of processed foods enriched with fruits and vegetables, which are affordable and convenient, can promote healthy eating behaviors among people living in Western countries. However, given the general perception that food processing reduces nutrient content, it is necessary to assess the bioaccessibility, bioavailability, dose-effect relationships, and bioactivity of nutrients and phytochemicals before commercializing processed food products. This randomized controlled trial evaluated the bioavailability and dose-effect of (poly)phenols from two blueberry varieties and a blueberry-rich protein bar. The main aim was to explore whether processed blueberry protein bars and unprocessed whole blueberries provide equivalent amounts of (poly)phenols following consumption. Blueberries are a rich source of (poly)phenols released from the fruit through digestion. Food matrix components such as fiber, sugars, starch, and protein can alter the release of (poly)phenols from blueberries during digestion. The gut microbiota also plays an important role in (poly)phenol bioavailability by breaking down unabsorbed (poly)phenols into smaller and more bioavailable compounds. The study also included a dietary compliance phase, where participants were asked to consume a diet low in (poly)phenols before and during each intervention to help control for background intake. However, as is common in free-living human studies, strict metabolic ward conditions were not used. Trial design The trial included 18 healthy adults who were randomly assigned to four interventions: two blueberry varieties (Elliott and Olympia), a blueberry-enriched protein bar, and a macronutrient-matched control beverage. Each participant underwent four interventions, one at a time, in a random sequence, and separated by a washout period. Blood and urine samples collected from participants were analyzed for (poly)phenols and related metabolites. Pharmacokinetics (maximum concentration and time at maximum concentration), bioavailability, and total urinary recovery of blueberry (poly)phenols were calculated using appropriate analytical methods. The primary outcome measured was the bioavailability of (poly)phenols, as assessed by total recovery in urine and area under the curve (AUC) in serum. The study was designed as a proof-of-concept and did not assess clinical health outcomes. Trial findings The trial found minimal differences in (poly)phenol bioavailability following consumption of Olympia or Elliott blueberries or a blueberry-rich snack bar made with Elliott berry. Notably, a similar urinary recovery of metabolites was observed across the treatments. More than 50% of metabolites showed no differences in clearance kinetics, despite the fact that blueberries and the snack bar had substantially different compositional profiles and bioaccessibility. Compared to Olympia blueberry, Elliott blueberry showed a slightly higher bioavailability, with three urinary (poly)phenolic metabolites exhibiting higher urinary recovery following its consumption. As previously reported, Elliott blueberry has a higher (poly)phenol composition and bioaccessibility than Olympia blueberry. These findings suggest that the genotype selection of blueberries based on differing bioaccessibility can successfully predict the delivery of higher amounts of (poly)phenolic metabolites from an equivalent serving size. As mentioned by researchers, the difference in bioavailability between blueberry varieties may be due to variations in bioaccessibility, which is influenced by food matrix components during digestion and absorption. (Poly)phenolic metabolites that increased in concentration from baseline showed similar total urinary recovery across the treatments. However, a difference in time of maximum serum concentration was observed for nearly 50% of metabolites, suggesting that kinetics is more variable than bioavailability. Notably, the trial revealed that the difference in bioavailability between the two blueberries is as significant as the difference observed between the berry and the protein bar. Cumulative urinary excretion of 68–81% of metabolites was similar between the Olympia and Elliott blueberries and the protein bar. These findings suggest that food processing methods have only a minimal impact on the overall bioavailability of blueberry (poly) phenols. Regarding urinary excretion kinetics, only a slight difference was observed between the Olympia berry and the Elliott blueberry-rich protein bar, suggesting that the bioaccessibility of blueberry or genetics may have a greater impact on bioavailability than food processing. It is important to note that the blueberry-rich protein bar tested in this study was produced using the same batch of Elliott blueberries as the whole berry intervention. The actual (poly)phenol content of the bars after processing was inferred based on the input berries, but not directly measured in the finished bars, which the authors acknowledge as a limitation. Furthermore, only one recipe and one processing method for the protein bar were evaluated. The protein bar was manufactured using a specialized protein-(poly)phenol aggregate processing methodology, which is thought to help retain more (poly)phenols compared to conventional snack bar production. The researchers cautioned that this trial investigated only two blueberry genotypes and one processing strategy. More research is needed to explore the impact of other variables on (poly)phenols' bioavailability and pharmacokinetics. For some metabolites, no significant differences were observed between berry-based interventions and control. This suggests that some (poly)phenolic metabolites measured in blood and urine may originate endogenously and are not entirely berry-derived. Significance The trial findings reveal that consuming different blueberry varieties with varying phytochemical compositions and bioaccessibilities, as well as blueberry-rich protein bars, can result in similar phytochemical bioavailability in the blood. These findings suggest that processed foods enriched with (poly)phenols, such as bars and snacks, may deliver (poly)phenols in similar amounts to raw fruits, which could support similar health benefits, although this was not assessed in this study. The blueberry-rich protein bar tested in the trial contains much higher amounts of (poly)phenols than commercially available blueberry-containing snack bars, likely due to its processing by protein-(poly)phenol aggregate methodology. However, the authors note that further studies are needed to investigate other blueberry varieties, additional food processing methods, and to directly measure the (poly)phenol content of processed products to determine the generalizability and translatability of these findings.