Drinking a chokeberry-rich juice daily may improve blood vessel function and prevent muscle loss during high-intensity training, offering a potential dietary strategy for people with pre-diabetes.

Study: Effects of two weeks of daily consumption of (poly)phenol-rich red berry fruit juice, with and without high-intensity physical training, on health outcomes in individuals with pre-diabetes mellitus. Image Credit: Flower_Garden / Shutterstock

A German study showed that daily intake of red berry fruit juice helped improve peripheral resistance, while its consumption combined with high-intensity physical training helped maintain muscle mass in pre-diabetic individuals. Notably, no significant changes were observed in glucose metabolism or markers of oxidative stress during the short intervention periods. The findings are published in the journal Nutrition, Metabolism, and Cardiovascular Diseases.

Background

Healthy lifestyle habits, including a healthy diet and regular physical activity, are associated with several health benefits. A combination of superfood intake and regular exercise has been found to reduce oxidative stress and inflammation and improve glycemic control in diabetic patients.

Polyphenols are a group of plant-based bioactive compounds with potent antioxidant and anti-inflammatory properties. Chokeberry juice is highly enriched with polyphenols, and its antioxidant capacity is four times higher than that of blueberry juice, cranberry juice, and red wine. Studies have shown a significant reduction in fasting blood glucose and glycated hemoglobin (a measure of glycemic control) levels in diabetic patients following the consumption of chokeberry juice.

With these health benefits, chokeberry juice may serve as a promising dietary intervention to prevent the progression of pre-diabetes mellitus to type 2 diabetes mellitus. In the current study, researchers assessed the health benefits of consuming a chokeberry-rich red berry fruit juice in pre-diabetic patients.

Study design

Ten pre-diabetic individuals participated in two crossover trials. These two main trial sections (Study Section A without exercise, and Study Section B with exercise) were separated by washout periods (one week for A, four weeks for B, and at least an 8-week washout period for the six individuals who participated in both sections).

For the first trial (Study Section A), participants were randomly assigned to the red berry drink (intervention) group and the placebo drink (control) group. Both drinks were consumed twice daily for 14 days. In this trial, participants were instructed to avoid regular physical exercise.

For the second trial (Study Section B), which also involved ten participants (six of whom had participated in Study Section A), they followed a similar crossover regimen of juice versus placebo, but this time it was combined with a high-intensity concurrent strength and endurance training. The training consisted of three sessions per week, including brisk walking and bodyweight strength exercises (like push-ups, rows, squats) using ‘Every Minute on the Minute’ (EMOM) and ‘As Many Repetitions As Possible’ (AMRAP) approaches.

The main aim of the trials was to assess the effect of red berry juice intake on body weight and composition, glucose metabolism, oxidative stress, arterial vessel stiffness, and peripheral resistance.

Graphical abstract

Study findings

The findings of the first trial (Study Section A), which assessed the health effects of 14-day red berry juice intake without an exercise intervention, revealed a significant reduction in peripheral resistance in participants who consumed the juice for 14 days. However, no significant change was observed in the placebo group.

The findings of the second trial (Study Section B), which assessed the health effects of 14-day red berry juice intake in combination with a high-intensity concurrent strength and endurance training, revealed a slight decline in relative muscle mass in the placebo group participants. In contrast, no significant change in relative muscle mass was observed in the intervention (red berry juice) group, suggesting a muscle-preserving effect. During this training phase, dietary recalls indicated that protein intake in both groups (around 0.92–0.96 g/kg body weight) was below the recommended levels for older adults engaged in strength training, which may have influenced muscle mass outcomes.

Study significance

The study highlights that short-term intake of a polyphenol-rich red berry fruit juice with a 25% chokeberry content may offer specific benefits for pre-diabetic individuals. Specifically, daily consumption of the juice alone was linked to improved peripheral resistance, while its intake combined with high-intensity physical exercise appeared to help maintain muscle mass.

In participants who consumed the red berry juice alone for 14 days (Study Section A), peripheral resistance was improved. Separately, a measure of arterial vessel stiffness (Pulse Wave Velocity) also showed improvement during this part of the study, but this was observed in both the juice and placebo groups. These findings highlight a potential beneficial effect of such interventions on cardiovascular health. The researchers suggest that the improvement in arterial vessel stiffness seen in both groups might be due to the substantial amount of potassium provided by both the red berry juice and the placebo drink.

The improvement in peripheral resistance, specifically in the juice group, could be attributed to polyphenols present in the red berry juice. Existing evidence indicates that polyphenol-dependent induction of gut microbiota diversity and reduction of systemic oxidative stress can lead to improved vascular health and increased bioavailability of nitric oxide, which in turn acts as a potent vasodilator.

Another notable finding of the study (from Study Section B) is that participants who consumed red berry juice maintained relative muscle mass during the training intervention, in contrast to the loss of relative muscle mass observed among placebo group participants undergoing the same training. This benefit may also be attributed to polyphenols, as these bioactive compounds are known to have muscle atrophy-preventing and muscle mass-preserving effects.

Previous studies investigating the effect of chokeberry intake on muscle mass have shown that chokeberry promotes multinucleated myotube formation in myoblasts through the PI3K/Akt/mTOR signaling pathway. This observation suggests a possible role of chokeberry in muscle tissue formation and growth.

The loss of relative muscle mass observed among placebo group participants during the training intervention might be associated with exercise-induced muscle damage, which is commonly observed among individuals who are not regularly engaged in physical activity. Exercise-induced accumulation of pro-inflammatory mediators and free radicals may also induce muscle damage.

The red berry juice used in this study contains approximately 25% chokeberry, and a 200 mL serving provides 820 mg of polyphenols. Participants consumed two such servings daily. A pure chokeberry juice, on the other hand, provides over 1200 mg of polyphenols per 200 mL. To avoid the sour, acidic, and astringent taste of chokeberry juice, the researchers added a substantial amount of grape juice to the red berry juice. This might also have health-related ergogenic effects, as they suggested.

Key limitations of the study include its small sample size (ten participants per trial section) and short duration (two weeks). The study also lacks information on participants’ baseline polyphenol intake through food sources other than the red berry juice provided. Furthermore, body composition was measured using bioelectrical impedance analysis (BIA), and the authors note that other methods like DXA might be useful for future confirmation. This information is vital for more precisely assessing the health benefits of red berry juice.

Further studies should explore long-term effects of chokeberry juice and similar interventions in a large group of individuals to further clarify underlying mechanisms.