The primary purpose is to test whether cocoa-rich bioflavanols can improve blood flow to the hand and fingers and improve hand function/dexterity during cold exposure. Secondary purpose is to understand whether bioflavanol supplementation can change the gut microbiome.

Loss of manual dexterity significantly impacts Warfighter effectiveness and lethality on the cold-weather battlefield. Identifying countermeasures that improve hand and finger temperatures, hand and finger blood flow, manual dexterity, and thermal comfort may lead to better Warfighter performance. A primary purpose of this study is to test the efficacy of a commercial off-the-shelf cocoa-rich bioflavanol product on hand/finger blood flow and temperature, manual dexterity, and thermal comfort during whole-body cold exposure. Another primary purpose is to determine the effect of bioflavanols on the finger cold-induced vasodilation (CIVD) response to cold-water immersion. Secondary purposes are to determine if: a) cocoa-rich flavanols stimulate the growth of beneficial gut bacteria and b) impact attention and effort perception during dexterity task completion in the cold. Two experimental studies (n = 20 in each study, 10 women and 10 men, 18-49 yr) will be conducted. Experiment #1 consists of immersing the middle finger in cold water (4°C) for 30 minutes; experiment #2 consists of whole-body cold exposure (8°C air, 90-min exposure, wearing cold-weather clothing but bare-handed). In both experiments, outcomes will be measured after both acute flavanol or placebo ingestion and chronic ingestion of flavanol/placebo (8 days of supplementation). Daily flavanol ingestion will be 900 mg/day. Volunteers will serve as their own controls in this crossover, double-blind research design. The washout period between flavanol and placebo treatments will be at least 2 weeks (longer for women who will be tested only during the follicular phase). Measurements during these tests include skin temperature, skin blood flow, fine and gross motor dexterity, thermal comfort, and effort perception. Fecal samples, in both experiments, will be collected before and after 8 days of cocoa-rich bioflavanol supplementation to examine if bioflavanol supplementation increases the number of beneficial bacteria in the gut microbiome. Information from this study will inform combat nutrition developers about the efficacy of cocoa-rich bioflavanols and possible inclusion into cold-weather field rations.

Inclusion Criteria:

• Age - 18-49 years (17-49 for active military).
• Refrain from the following for 2 weeks before and during the study (including the washout period): consumption of flavanol rich foods including cocoa, chocolate, apples, red, white, and sweet wine, apricots, blueberries, peaches/nectarines, plums, grapes, strawberries, pecans (no more than ½ cup/day, pistachios, (no more than ½ cup per day), and apple juice.
• Participants not to change their daily intakes of tea (green or black) or coffee.

Exclusion Criteria:

• History of cold injuries.
• Raynaud's syndrome.
• Cold-induced asthma/bronchospasm
• Difficulty swallowing pills.
• Previous hand/finger injuries that impair dexterity and hand function.
• Metal hardware (plates/screws) in the forearms and hands.
• Blood donation in last 8 weeks.
• Medicine use (including any over the counter medication such as Tylenol, Advil, Sudafed, etc…), with the exception of birth control and a multi-vitamin.
• Known allergies to medical adhesives or cocoa/chocolate.
• History of disease of the gastrointestinal tract including (but not limited to) diverticulosis, diverticulitis and inflammatory bowel disease, peptic ulcer disease, Crohn's disease, ulcerative colitis; or previous gastrointestinal surgery.
• No planned MRI during the study or within 2 days after completing a cold test.
• Use of dietary supplements (to include probiotics and prebiotics), with exception of multi-vitamin containing up to 100% of the recommended daily allowance (RDA).
• No exercise or smoking within 8 hours of testing.
• Pregnant or breastfeeding.
• Oral antibiotic use within 3 months of study participation.
• Inability or unwillingness to not consume fermented food products or prebiotic-containing food products for 2 weeks prior to and throughout study participation. Examples include kefir, kombucha, aged cheese, pickles, sauerkraut, sour cream, tempeh, yogurt, kimchi, miso, vinegar, sourdough bread, wine and beer.
• Colonoscopy within 3 months of study participation.
• On average has a bowel movement less frequently than every other day.

Double-blind