Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, C063

Oral Communications

Resting metabolic rate in vegetarians and omnivores before and after inhibition of the oral nitrate/nitrite pathway

R. Bescos Garcia1, A. Ashworth1, C. Easton2, L. Liddle2

1. University of Plymouth, Plymouth, United Kingdom. 2. University of the West of Scotland, Paisley, United Kingdom.


Low energy density of vegetarian diets has been suggested to induce a reduction in the resting metabolic rate (RMR) of individuals following this dietary pattern. This can also be a key factor to explain the impact of these diets in the management of obesity. However, other factors such as dietary nitrate (NO3) intake may play a significant role on the modulation of the RMR through the nitrate/nitrite/nitric oxide pathway (1). Thus, the main aim of this study was to estimate dietary energy and NO3 consumption in a group of vegetarians and omnivores, and its effect on the RMR before and after the inhibition of the oral nitrate/nitrite pathway. Twenty-two healthy subjects following a vegetarian diet (V) for at least a year (16 F + 6 M) and 19 omnivores (O) (11 F + 8 M) of similar age (V= 26 ± 6; O= 26 ± 6 y/o), BMI (V= 22.9 ± 3.8; O= 22.1 ± 2.9), gender and levels of moderate and vigorous physical activity (V= 315 ± 221; O= 334 ± 208 min/w) participated in this study. They recorded all their food consumption for seven days using food diaries while they used a placebo mouthwash (water) to rinse their mouth twice a day (1 min). On the seventh day, a saliva and blood sample were collected under fasting conditions before the RMR was assessed with an indirect calorimetric system connected to a ventilated hood (Jaeger Oxycon Pro) for 30 min. Then, participants were given antibacterial mouthwash (Corsodyl, UK) for seven more days in order to inhibit the oral NO3/NO2 pathway following a single-blind and non-randomized design. They were also encouraged to replicate their food intake from the previous week. The same measurements were taken under fasting conditions on the fourteenth day. Results are expressed as mean ± SD. Energy intake was slightly higher but not statistically different (P>0.05) in omnivores (2,021 ± 560 kcal) than in vegetarians (1,827 ± 526 kcal). Dietary NO3 intake was greater in vegetarians (97 ± 79 mg/day) than in omnivores (78 ± 47 mg/day), but this was not statistically different (P>0.05). No differences were found (P>0.05) in plasma NO3 (V= 43 ± 33 µM; O= 40 ± 18 µM) and NO2 (V= 84 ± 41 nM; O=74 ± 21 nM) and salivary NO3 (V= 525 ± 698 µM; O= 542 ± 571 µM) and NO2 (V= 329 ± 340 nM; O= 319 ± 283 nM) between both groups after using placebo. The RMR was also similar in both groups under placebo conditions (V= 1,396 ± 254 kcal; O= 1,397 ± 304 µM). A significant reduction (P<0.05) of plasma NO2 (V= 65 ± 15 nM; O= 61 ± 16 nM) and salivary NO2 (V= 155 ± 171 nM; O= 133 ± 214 nM) was observed in vegetarians and omnivores after using antibacterial mouthwash indicating a significant inhibition of the oral nitrate/nitrite pathway. However, this did not affect the RMR in either group (V= 1,404 ± 255 kcal; O= 1,401 ± 318 kcal). These data suggest that vegetarian diets do not reduce the RMR compared to an omnivore healthy diet. Additionally, the oral nitrate/nitrite pathway does not seem to be a key regulator of RMR in vegetarians and omnivores.

Where applicable, experiments conform with Society ethical requirements