Popeye was right: Could nitrate-rich spinach enhance strength & fitness?

By Will Chu

- Last updated on GMT

The team hypothesised that performing sprints in low-oxygen conditions with oral nitrate intake, might yield physiological adaptations to boost exercise performance.©iStock/Lecic
The team hypothesised that performing sprints in low-oxygen conditions with oral nitrate intake, might yield physiological adaptations to boost exercise performance.©iStock/Lecic
Diet supplementation with nitrates, such as those found in spinach and beetroot could enhance sporting performance, a study has found.

Subjects took nitrate supplements whilst taking part in intense cycling sessions three times a week, recording a change in muscle fibre make up in response to nitrate intake when training under low oxygen conditions.

The study raises the question of whether this adaptation to fast-oxidative type IIa muscle fibres [slow twitch] can eventually enhance exercise performance.

Type IIa fibres [fast twitch] are less fatigue resistant, produce more muscular power in a short period of time, contracting at a faster speed than slow twitch fibres.

Slow twitch fibres are more suited to endurance events like road cycling; fast twitch to power events like weightlifting and sprinting.

Muscle adaptations

gym sports muscle
Individuals who show muscle makeup of mostly type IIa fibres have better sporting performance in sports such as weightlifting.©iStock

Researchers from the University of Leuven in Belgium took 27 relatively fit subjects and placed them into one of three experimental conditions: sprint interval training (SIT) conducted in an environment with normal oxygen levels (20.9%), SIT conducted in low oxygen levels (15%) and SIT in low oxygen levels with nitrate supplementation. A placebo group was also included.

The individuals were subjected to five weeks of SIT on a cycle (30-s sprints mixed with four and a half min recovery intervals, three weekly sessions, four–six sprints per session),  

Nitrate (6.45 mmol sodium nitrate) or placebo supplements were given three hours before each session.

At the start and end of the trial, SIT participants performed a VO2max-test. This consisted of a 30-min simulated cycling time-trial, as well as a 30-s cycling sprint test. Muscle biopsies were then taken.

Findings revealed the number of type IIa fibres increased in those exercising in a low oxygen environment and taking the nitrate capsules. Other groups remained unchanged. VO2max and 30-min time-trial performances increased in all groups.

“This study demonstrates that a simple nutritional supplementation strategy, i.e. oral nitrate intake, can impact on training-induced changes in muscle fibre composition,"​ said professor Peter Hespel from the Athletic Performance Centre at the University of Leuven.

"However, consistent nitrate intake in conjunction with training must not be recommended until the safety of chronic high-dose nitrate intake in humans has been clearly demonstrated."

Nitrates in the professional arena

football sports athletes active
Nitrate use in a professional environment was successfully put to the test with the Premiership title-winning Leicester City. ©iStock

Oral nitrate supplementation has been the subject of a number of studies all eager to investigate this compound’s potential as a sports nutrition supplement.

Inorganic nitrate is abundant in green leafy vegetables and beetroot. Following ingestion, this nitrate is converted in the body to nitrite and stored and circulated in the blood.

Dietary nitrate supplementation increases plasma nitrite concentration and reduces resting blood pressure. In low oxygen conditions, it is thought to be converted into nitric oxide, which plays a central role in vascular and metabolic control.

An emerging area of research has looked at how nitrate supplementation reduces the oxygen cost of submaximal exercise and how this can improve exercise tolerance and performance

The benefits of beetroot’s nitrate content have already alerted nutritionists at professional sports clubs in Europe.

Back in May, English Premier League champions Leicester City said beetroot​ ​juice consumption helped the underdog team keep its small squad fit and healthy.

Source: Frontiers in Physiology

Published online ahead of print, doi.org/10.3389/fphys.2016.00233

“Nitrate Intake Promotes Shift in Muscle Fiber Type Composition during Sprint Interval Training in Hypoxia.”

Authors: Peter Hespel et al.

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