Potato Intake Compared to Refined Grains in Healthy Adults: Cardiometabolic Risk Factors, Dietary Intake, Gut Microbiota and Short Chain Fatty Acids

Open Access
- Author:
- Johnston, Emily A
- Graduate Program:
- Nutritional Sciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 13, 2020
- Committee Members:
- Penny Margaret Kris-Etherton, Dissertation Advisor/Co-Advisor
Penny Margaret Kris-Etherton, Committee Chair/Co-Chair
Barbara Jean Rolls, Committee Member
Kathleen Loralee Keller, Committee Member
Darrell William Cockburn, Outside Member
Kristina Susan Petersen, Special Member
Laura E Murray-Kolb, Program Head/Chair - Keywords:
- potato
fasting glucose
cardiometabolic health
supplemental feeding study
resistant starch
microbiota - Abstract:
- Observational studies commonly show potato intake is associated with increased risk of cardiometabolic disease, but clinical trials have not confirmed these findings. Potatoes are a low cost source of important short-fall nutrients in the American diet including potassium and fiber and they also contribute resistant starch (RS) to the diet. RS is a fermentable fiber that is associated with increased satiety and improved measures of glycemia in controlled studies, but intake in the US is low. Notably, RS intake may enhance levels of short chain fatty acid (SCFA) - producing bacteria in the gut. SCFA are associated with decreased cardiometabolic risk. As such, it is important to understand the health effects of potato consumption, compared to commonly consumed refined grains, as part of a standard American diet. The guiding aim of this dissertation was to describe the effects of potatoes on cardiometabolic health outcomes, diet quality and gut microbial changes relative to refined grains. It was hypothesized that no difference in cardiometabolic endpoints would be detected between conditions, but diet quality and RS intake would increase with potato consumption. Healthy participants on self-selected diets received one potato-based side dish or one refined grain-based side dish daily, for four weeks, separated by a minimum two-week break. All study dishes were matched for calories and carbohydrates and prepared without excess saturated fat or sodium. Participants were instructed to consume the side dish with a meal in place of a habitual carbohydrate-containing side dish. Biochemical outcomes (markers of glycemic control, lipids/lipoproteins), weight, blood pressure (BP) and measures of arterial stiffness (pulse wave velocity (PWV)) were assessed at baseline and condition endpoints. Dietary intake and fecal samples were collected at baseline and at the midpoint and endpoint of each condition. Diet quality was measured using the Automated Self-Administered 24-hour recall and calculated using the Healthy Eating Index (HEI)-2015. Fecal samples were analyzed for RS- degrading bacteria, SCFA-producing bacteria, SCFA concentration, alpha and beta diversity. Fifty healthy adults (female n=34; age: 40±13; BMI: 24.5±3.6 kg/m2) completed this study. There were no between-condition differences in the primary outcome, fasting plasma glucose (-0.97; mg/dL, 95% CI: -2.3, 0.35; p=0.15), or any biochemical or vascular outcomes. The total HEI-2015 score was higher during the potato condition compared to the refined grain condition [POT: 55.8 (95% CI: 52.6, 59.0); REF: 52.3 (95% CI: 49.1, 55.6); p=0.01], as were potassium intake [POT: 3044 mg (95% CI: 2809, 3279); REF: 2497 mg (95% CI: 2260, 2733); p<0.001) and fiber intake [POT: 21 g (95% CI: 19, 23); REF: 18 g (95% CI: 16, 20), p=0.01]. Potato dishes contained greater amounts of resistant starch, on average, than the refined grain dishes [POT: 1.31% wet basis (95%CI: 0.94, 1.71); REF: 0.73% wet basis (95%CI: 0.34, 1.14); p=0.03]. Potato dishes contained 2 to 2.9 g RS per serving, while refined grain dishes contained 0.2 to 1.2 g. Fecal samples were analyzed for relative abundance of resistant starch degrading and butyrate-producing bacteria, SCFA and alpha and beta diversity. Bacteria from the Roseburia spp. were present in greater abundance in the potato condition [POT: 1.25% (95% CI: 0.98, 1.52); REF: 1.03% (95% CI: 0.76, 1.30), p=0.02)]. The bacterial species Alistipes putredinis was present in greater abundance during the refined grain condition [POT: 0.007% 95% CI: 0.005, 0.009); REF: 0.012% (95% CI: 0.009, 0.014), p=0.02]. No significant differences were observed in relative abundance of species known to degrade RS or produce SCFA, SCFA concentration or alpha or beta diversity. In healthy adults, intake of one medium-sized potato per day for four weeks did not affect markers of cardiometabolic health compared to one serving of refined grains. Intake of potatoes was associated with better diet quality than intake of refined grains, and with higher intake of potassium and fiber, two shortfall nutrients in the American diet. Desirable changes were seen in relative abundance of butyrate-producing bacteria in fecal analyses. Intake of steamed or baked potatoes without the addition of excess saturated fat or sodium in a healthy portion size can be a part of a healthful diet and may facilitate meeting dietary recommendations.