Gymnastik- och idrottshögskolan, GIH

BACKGROUND: Inorganic nitrate from dietary sources has raised health concerns due to its possible conversion into carcinogenic N-nitrosamines, leading to strict regulations on nitrate concentrations in food and drinking water.

OBJECTIVES: In this study, which was a part of a larger randomized controlled trial, we evaluated urinary excretion of N-nitrosamines in response to daily dietary nitrate intake over a 5-wk period using 2 different forms of nitrate administration.

METHODS: A total of 231 participants with mild hypertension were randomly assigned into 3 groups. Group 1 (n = 78) consumed vegetables low in nitrate along with a placebo capsule (300 mg potassium chloride). Group 2 (n = 77) consumed the same low-nitrate vegetables plus a potassium nitrate supplement (300 mg). Group 3 (n = 77) consumed nitrate-rich leafy green vegetables providing 300 mg nitrate daily plus the placebo capsule. Twenty-four-hour urine samples were collected before and after the intervention. Nitrate was measured with high-pressure liquid chromatography and N-nitrosamine concentrations were quantified using ultra high-pressure liquid chromatography-tandem mass spectrometry. A paired t-test was used for statistical analyses.

RESULTS: As expected, urinary nitrate increased ∼5- to 6-fold in participants consuming nitrate-rich vegetables or potassium nitrate compared with those consuming potassium chloride. Total urinary excretion of N-nitrosamines was low across all groups under basal conditions (<5 μg/24 h) and did not significantly change after the intervention. A similar lack of change was observed for each of the 7 individual N-nitrosamine species measured.

CONCLUSIONS: These findings suggest that a 5-wk dietary intake of nitrate mostly exceeding the current consensus for upper limit of the acceptable daily intake (3.7 mg/kg/d), whether provided as a vegetable source or as a nitrate salt, does not increase urinary excretion of N-nitrosamines. This study was registered at clinicaltrials.gov as NCT02916615.

Glucosinolate-rich red kale sprouts (GRS) combined with intense exercise training for 7 days reduce blood lactate during exercise, attenuate hypoglycemic events, improve performance, and reduce markers of oxidative stress. This study aimed to investigate the acute, dose-dependent effects of GRS on blood lactate and blood glucose after ingestion of two different doses. In the study, healthy participants (n = 15) consumed 37.5 or 75 g of GRS or an isocaloric placebo blended into a beverage on three occasions. They cycled on an ergometer at three submaximal work rates (~100, ~120, ~140 W, respectively) before and 3 h after ingestion of GRS. Oxygen uptake, substrate-level oxidation, blood lactate, blood glucose, and ratings of perceived exertion were taken before and after each interval. GRS intake acutely decreased blood lactate during submaximal cycling and increased resting blood glucose. The largest lactate reduction occurred at 37.5 g compared to placebo, with concentrations 0.4 ± 0.6 mM lower at the highest work rate (p = 0.00175). For 75 g, the reduction was 0.3 ± 0.5 mM (p = 0.0484). No significant effects appeared at the lowest work rate. Resting blood glucose averaged 3.9 ± 0.3 mM after placebo compared to 4.3 ± 0.4 mM after 37.5 g and 4.3 ± 0.4 mM after 75 g GRS (p < 0.0001, respectively). In conclusion, these findings suggest that acute intake of a glucosinolate-rich beverage may influence lactate and glucose metabolism, with lower blood lactate concentrations observed at two submaximal work rates and altered blood glucose concentrations at rest.

This is a secondary analysis of a non-randomized controlled six-month trial concerning the effects of the 5:2 diet on cardiovascular risk factors (blood pressure, blood lipids, adipokines and inflammatory markers) in overweight or obese individuals with and without type 2 diabetes (T2D). Ninety-seven individuals were recruited, 35 with T2D and 62 without (controls). Ninety-three completed six months of the 5:2 diet, consisting of 2 days of fasting (500 kilocalories (kcal) for women and 600 kcal for men) and five days of their regular diet. A total of 82 participants (31 with T2D and 51 controls) attended the 12-month follow-up. After the six-month intervention, both groups lost body weight (-6.3% in the T2D group and -5.0% among controls). There were significant improvements in waist circumference, blood pressure, high-density lipoprotein cholesterol (HDLchol), low-density lipoprotein cholesterol (LDLchol) and serum levels of adiponectin. In addition, participants with T2D had decreased alanine transferase (ALT) and high-sensitive C-reactive protein (hsCRP), which were significantly different from the control group. The control group had significant decreases in triglycerides and leptin concentrations. At the 12-month follow-up, improvements remained for HDLchol and adiponectin in both groups. In addition, the T2D group had significantly decreased hsCRP and leptin concentrations and the control group showed a significant decrease in ALT. In conclusion, a six-month 5:2 diet resulted in significant improvements in cardiovascular risk factors in overweight or obese participants with and without T2D, with several improvements persisting at 12 months. Individuals with T2D appeared to gain somewhat greater metabolic benefits from the intervention than the control group.

This non-randomized controlled trial aimed to compare the effect of the 5:2 diet on insulin levels as a primary outcome and markers of insulin secretion (connecting peptide (C-peptide) and insulin-like growth factor binding protein-1 (IGFBP-1)) and sensitivity (Homeostatic Model Assessment for Insulin Resistance (HOMA-IR)), as well as body composition as secondary outcomes in overweight/obese individuals with and without type 2 diabetes (T2D). Ninety-seven participants (62% women), 35 with T2D and 62 BMI- and waist-matched controls without T2D, followed the 5:2 diet (two days per week of fasting) for six months with a 12-month follow-up. At six months, there was no loss to follow-up in the T2D group, whereas four controls discontinued this study. Overall, 82% attended the 12-month follow-up. After the intervention, insulin levels decreased in the control group and glucose decreased in the T2D group, while C-peptide, HOMA-IR, waist circumference, BMI, trunk, and total fat% decreased in both groups. Furthermore, low IGFBP-1, indicating hyperinsulinemia, improved in the T2D group. The changes in fasting glucose and waist measurement were significantly more improved in the T2D group than in the controls. Persistent positive effects were observed at the 12-month follow-up. The 5:2 diet for six months was feasible and efficient to reduce markers of insulin secretion and resistance and therefore holds promise as management of overweight/obesity in subjects with and without T2D.

BACKGROUND: Green leafy vegetables (GLV) contain inorganic nitrate, an anion with potential prebiotic effects on the oral microbiome. However, it remains unclear whether GLV and pharmacological supplementation [potassium nitrate (PN)] with a nitrate salt induce similar effects on the oral microbiome.

OBJECTIVES: This study aimed to compare the effect of GLV with PN supplementation on the oral microbiome composition and salivary biomarkers in individuals with high blood pressure.

METHODS: Seventy individuals were randomly allocated to 3 different groups to follow a 5-wk dietary intervention. Group 1 consumed 300 mg/d of nitrate in form of GLV. Group 2 consumed pills with 300 mg/d of PN and low-nitrate vegetables. Group 3 consumed pills with potassium chloride (placebo: PLAC) and low-nitrate vegetables. The oral microbiome composition and salivary biomarkers of oral health were analyzed before and after the dietary intervention.

RESULTS: The GLV and PN groups showed similar microbial changes, probably nitrate-dependent, including an increase in the abundance of Neisseria, Capnocytophaga, Campylobacter species, and a decrease in Veillonella, Megasphaera, Actinomyces, and Eubacterium species after the treatment. Increased abundance of Rothia species, and reduced abundance of Streptococcus, Prevotella, Actinomyces, and Mogibacterium species were observed in the GLV group, which could be nitrate-independent. GLV and PN treatments increased salivary pH, but only GLV treatment showed an increase in the salivary buffering capacity and a reduction of lactate.

CONCLUSION: The combination of nitrate-dependent and nitrate-independent microbial changes in the GLV group has a stronger effect to potentially improve oral health biomarkers compared with PN.

Oxidative stress plays a vital role for the adaptive responses to physical training. However, excessive oxidative stress can precipitate cellular damage, necessitating protective mechanisms to mitigate this effect. Glucosinolates, found predominantly in cruciferous vegetables, can be converted into isothiocyanates, known for their antioxidative properties. These compounds activate crucial antioxidant defence pathways and support mitochondrial function and protein integrity under oxidative stress, in both Nrf2-dependent and independent manners. We here administered glucosinolate-rich broccoli sprouts (GRS), in a randomized double-blinded cross-over fashion to 9 healthy subjects in combination with daily intense exercise training for 7 days. We found that exercise in combination with GRS significantly decreased the levels of carbonylated proteins in skeletal muscle and the release of myeloperoxidase into blood. Moreover, it lowered lactate accumulation during submaximal exercise, and attenuated the severe nocturnal hypoglycaemic episodes seen during the placebo condition. Furthermore, GRS in combination with exercise improved physical performance, which was unchanged in the placebo condition.

Red blood cells (RBCs) mediate cardioprotection via nitric oxide-like bioactivity, but the signaling and the identity of any mediator released by the RBCs remains unknown. We investigated whether RBCs exposed to hypoxia release a cardioprotective mediator and explored the nature of this mediator. Perfusion of isolated hearts subjected to ischemia-reperfusion with extracellular supernatant from mouse RBCs exposed to hypoxia resulted in improved postischemic cardiac function and reduced infarct size. Hypoxia increased extracellular export of cyclic guanosine monophosphate (cGMP) from mouse RBCs, and exogenous cGMP mimicked the cardioprotection induced by the supernatant. The protection induced by hypoxic RBCs was dependent on RBC-soluble guanylate cyclase and cGMP transport and was sensitive to phosphodiesterase 5 and activated cardiomyocyte protein kinase G. Oral administration of nitrate to mice to increase nitric oxide bioactivity further enhanced the cardioprotective effect of hypoxic RBCs. In a placebo-controlled clinical trial, a clear cardioprotective, soluble guanylate cyclase-dependent effect was induced by RBCs collected from patients randomized to 5 weeks nitrate-rich diet. It is concluded that RBCs generate and export cGMP as a response to hypoxia, mediating cardioprotection via a paracrine effect. This effect can be further augmented by a simple dietary intervention, suggesting preventive and therapeutic opportunities in ischemic heart disease.

AIM: The inorganic anions nitrate and nitrite are oxidation products of nitric oxide (NO) that have often been used as an index of NO generation. More than just being surrogate markers of NO, nitrate/nitrite can recycle to bioactive NO again. Nitrate is predominantly eliminated via the kidneys; however, there is less knowledge regarding tubular handling. The aim of this study, as part of a large randomized controlled trial, was to explore potential sex differences in renal nitrate handling during low and high dietary nitrate intake. We hypothesized that renal clearance and excretion of nitrate are higher in men compared to women.

METHODS: In prehypertensive and hypertensive individuals (n = 231), nitrate and nitrite were measured in plasma and urine at low dietary nitrate intake (baseline) and after 5 weeks supplementation with nitrate (300 mg potassium nitrate/day) or placebo (300 mg potassium chloride/day). Twenty-four hours ambulatory blood pressure recordings and urine collections were conducted.

RESULTS: At baseline, plasma nitrate and nitrite, as well as the downstream marker of NO signalling cyclic guanosine monophosphate, were similar in women and men. Approximately 80% of filtered nitrate was spared by the kidneys. Urinary nitrate concentration, amount of nitrate excreted, renal nitrate clearance (C_nitrate ) and fractional excretion of nitrate (FE_nitrate ) were lower in women compared to men. No association was observed between plasma nitrate concentrations and glomerular filtration rate (GFR), nor between FE_nitrate and GFR in either sex. After 5 weeks of nitrate supplementation plasma nitrate and nitrite increased significantly, but blood pressure remained unchanged. FE_nitrate increased significantly and the sex difference observed at baseline disappeared.

CONCLUSION: Our findings demonstrate substantial nitrate sparing capacity of the kidneys, which is higher in women compared to men. This suggests higher tubular nitrate reabsorption in women but the underlying mechanism(s) warrants further investigation.