Dietary advice focused on increasing dietary nitrate intake in active individuals

Recent research has shown that intake of nitrate (NO3) can lead to an increase
in plasma nitrite and nitrate levels, and a reduction in blood pressure at rest
and pulmonary oxygen uptake during exercise. These effects are related to the
endogenous production of nitric oxide (NO), which is associated with a rise in
plasma nitrite levels.

The consumption of vegetables declared for 60-80% of the daily intake of
nitrate. So far, most studies mainly using sodium nitrate (NaNO3) and red beet
juice to induce these metabolic effects. A recent study from our group shows
that acute supplementation of nitrate-rich vegetables can provide the same
effects as sodium nitrate and red beet juice on the rise in plasma nitrite and
nitrate values **and a reduction in blood pressure. However, there is yet no
knowledge whether prolonged intake of nitrate via the usual diet can show the
same effects. In addition, it is not known whether taking those quantities of
vegetables are practicable.

Based on the gaps in current literature, our main goal will therefore be to
gain further insight into the effect of 7 days supplementation with
concentrated nitrate-rich beet juice compared with dietary advice aimed at
increasing the nitrate intake through the habitual diet.

The aim of the current study is to compare the effects of supplementation with
concentrated nitrate-rich beetroot juice versus dietary advice to increase
dietary nitrate intake through the habitual diet. Therefore, we will assess the
impact of 1-wk concentrated beetroot juice supplementation vs 1-wk of dietary
advice to increase vegetables consumption on plasma and saliva nitrate and
nitrite concentrations, blood pressure, urinary nitrosamine formation, and
dietary nitrate intake.

Randomized, crossover intervention study

Participants will receive 1-wk of dietary guidance in which they will be
provided with a sufficient amount of vegetables, representing 400 mg (6.5 mmol)
nitrate per serving (i.e. each day), including information about nitrate and
nitrate rich recipes. In a randomized cross-over manner, participants will also
follow a 1-wk supplementation protocol in which they will ingest 400 mg (6.5
mmol) nitrate per day in the form of concentrated red beetroot juice. Both
trials will be separated by a 1-wk washout period.

Participants will be required to report to the laboratory for a total of 11
visits for a total of maximally 15 hours, including a screening session. Prior
to the first experimental visit, participants will be asked to record their
diet for 7 days and refrain from strenuous physical exercise or labour for the
24h preceding the visit. Participants will be asked to avoid caffeine and
alcohol for 12h and 24h preceding each visit, respectively.

They will be asked to refrain from exercise for the 24h prior to subsequent
visits. In total, participants will donate ten blood samples, representing ~7.5
mL over the course of 4 weeks. Insertion of the needle for blood sampling could
result in a small hematoma. Participants also have to perform three 24h urine
collections. In addition, the main time commitment will consist of filling in
three 7-day food diaries.
The administered dose of nitrate in beetroot juice has been used in multiple
clinical and exercise studies and is a commercially available supplement. The
most commonly reported side effect is beeturia (red-coloured urine/faeces,
15-20% of the population) and mild gastrointestinal distress (bloating,
belching), and occasional reports of mild headache (which may or may not be
associated with the nitrate). The vegetables used in the present study are
freely available natural products. The only comparison available is from the
ingestion of nitrate-rich beverages, which has been described to lead to mild
gastrointestinal distress (bloating, belching) in some cases. The long term
effects of nitrate ingestion still need to be fully investigated.

There is no direct benefit for the participants, only their contribution to
scientific knowledge and the provision of vegetables.