Beetroot as a functional food with huge health benefits: Antioxidant, antitumor, physical function, and chronic metabolomics activity (2024)

A review of the latest research on the biological activities of nutritional composition in beetroot including antioxidant, antitumor, physical function, chronic metabolomics activity, and other functions.

2.1. Antioxidant activity

Since the emergence of processed foods, the demand for that has never decreased. It has also become increasingly common to add a certain amount of antioxidants to processed foods. Especially today, it is more urgent to make full use of antioxidants to extend shelf life and ensure food quality for many processed foods that are rich in high protein and fat (Ranawana etal.,²⁰¹⁸). Although many synthetic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are widely used in the world, natural antioxidants are highly sought after at home and abroad for their possible greater safety and health‐promoting effect (Liu etal.,²⁰¹⁵; Wettasinghe etal.,²⁰⁰²). Polyphenols and anthocyanin both belong to natural antioxidants, even exhibiting much stronger antioxidant capacity than BHA and BHT (Guitard etal.,²⁰¹⁶; Narayan etal.,¹⁹⁹⁹). In addition, the antioxidant capacity of betanin, the major betalains in beetroot, is gradually receiving greater attention in response to public health demands. It is one of the few red dyes approved for food manufacturing known as E162 (Kapadia etal.,²⁰¹¹). Its antioxidant ability is also constantly being researched and reported. Some studies have even shown that the free radical scavenging ability of betanin in beetroot is nearly twice as high as some anthocyanins under the circ*mstance of pH >4 (Borkowski etal.,²⁰⁰⁵). The free radical scavenging ability and high antioxidant activity of betanin are linked to the presence of phenolic hydroxy groups in the structure (Costa etal.,²⁰¹⁷). Previous reports have also indicated that the antioxidant activity of betanin is associated with the rich unsaturated bonds on the benzene ring (Butera etal.,²⁰⁰²). As for the specific active functional groups, further research and confirmation are needed.

Apart from having betanin, beetroot also contains a considerable amount of polyphenols and phenolic, a small quantity of vitamin C and vitamin E, which have been proved with the great antioxidant ability (Apak etal.,²⁰⁰⁴). Since betanin is the main active ingredient in beetroot, the researches on the antioxidant activity of beetroot are mainly concentrated upon betanin, and a small number of studies focus on the antioxidant activity of polyphenols (Koss‐Mikołajczyk etal.,²⁰¹⁹). Studies have indicated the content of total polyphenols in methanol extracts of pulp waste from beetroot ranged from 67 to 110mg TAE (tannic acid equivalents)/100g sample, which was higher than ethanol extract and aqueous extract (Wettasinghe etal.,²⁰⁰²).

In spite of the fact that beetroot has been widely used as a colorant in food and provides antioxidant protection to a certain extent simultaneously, it is relatively rare for the main purpose of serving as antioxidant rather than food colorant to add into processed food. Research on how to maximize the antioxidant potency of beetroot is also in its infancy. Vikas Kumar et al. once used the beetroot pomace extract to develop ginger sugar, hoping to compensate for the defects in the antioxidant capacity damage of ginger‐based products caused by blanching technology (Kumar etal.,²⁰¹⁸). It was found that optimum conditions for optimal oxidation titer of the ginger product were 7.81min of blanching time and 9.24% concentration with 0.905 desirabilities of beetroot pomace extract. In this case, its antioxidant activity could reach to 88.44% and the content of phenolics and betalains was high as 273.29mg/100g and 31.54mg/100g, respectively. Another study found that in sponge cakes, the combination of beetroot and chocolate further improved the polyphenol profiles, oxidative stability, and extended its shelf life (Ranawana etal.,²⁰¹⁸). It is mainly due to the fact that chocolate is more effective in retarding lipid oxidation than beetroot. This study is hopeful to provide a reference for the future combination of beetroot and these substances with good anti‐lipid oxidation capacity. Beyond that, the different processing type of beetroot also has a great influence on its antioxidant capacity. Burcu Guldiken et al. compared the effects of different processing methods including fresh samples, boiled, pickled, oven‐dried, pureed, jam‐processed, and juice‐processed on antioxidant activity (Guldiken etal.,²⁰¹⁶). It was found that fresh, dried, and pureed beetroot exhibited the highest TP (total phenolic), TF (total flavonoid), and TAC (total antioxidant capacities) values. In recent years, it was then reported that freezing with liquid nitrogen resulted in greatest increase in TP of beetroot (Dalmau etal.,²⁰¹⁹). Anne Porto Dalla Costa et al. pointed out that beetroot waste flour was a convenient processing method. It was advised to dry at 70 ℃ to obtain the maximum amount of betalains content and the best antioxidant activity (Costa etal.,²⁰¹⁷).

In addition to the above‐mentioned function of using beetroot as an antioxidant in food, more researches currently focus on the maintenance of balance by beetroot to counteract oxidative stress, thereby preventing and treating human diseases. Betanin in beetroot was reported both to be a free radical scavenger and an inducer of antioxidant defense mechanisms in cultured cells (Esatbeyoglu etal.,²⁰¹⁴). It could scavenge DPPH (2,2diphenyl‐1‐picrylhydrazyl), hydroxyl‐radicals, superoxide, and galvinoxyl in a concentration‐dependent manner and prevent DNA damage induced by hydrogen peroxide. The study revealed that Nrf2 (nuclear factor (erythroid‐derived 2)‐like 2) was the most likely involved signaling pathway that mediated the antioxidant activity. The transactivation of Nrf2 would then result in an increase of HO‐1 (HemeOxygenase), GSH (glutathione) proteins, and transactivation of PON1 (paraoxonase 1). As to whether such signal transduction pathway exists in the human body, there is no relevant proof yet. It was reported that under the gastrointestinal condition, betalains would remain stable without any significant loss in antioxidant properties, which further maintained the efficacy of beetroot for human disease treatment (Frank etal.,²⁰⁰⁵). To evaluate the antioxidant activity of beetroot, Malgorzata Kujawska et al. used a model of oxidative stress induced by two xenobiotics, N‐nitrosodiethylamine (NDEA), and carbon tetrachloride (CCl4) (Kujawska etal.,²⁰⁰⁹). The level of microsomal lipid peroxidation in rats pretreated with beetroot juice was found to decrease by 38%, while it was increased by several folds in rats administered with CCl4 alone. The reduced level of plasma protein carbonyls and diminished DNA damage in rats pretreated with beetroot juice before NDEA administration was similar to be detected. Additionally, pretreatment with beetroot juice caused a threefold increase in the activity of superoxide dismutase, reversing the downregulation of superoxide dismutase caused by oxidative stress model. This study has led the authors to believe that beetroot does possess promising antioxidant activity. As for the relevant antioxidants, it has not been elaborated and speculated that it might be the synergy of betalains and other compounds. Besides, betalains in beetroot have also been shown to inhibit oxidative metabolism of neutrophils in humans (Zielińska‐Przyjemska etal.,²⁰⁰⁹), enhance the activity of the antioxidant enzymes, superoxide dismutase, and peroxidase in irradiated mice liver, spleen, and kidney (Wroblewska etal.,²⁰¹¹). Apart from protecting cells from oxidative stress, it has been found that beetroot contributes to protecting cells from nitrative stress. In the study by Yasuko Sakihama et al., betanin in beetroot was proved to inhibit the nitration of peroxynitrate mediated by tyrosine in vitro (Sakihama etal.,²⁰¹²). Previous research suggested that beetroot weakened the activation and nuclear translocation of NF‐κB to resist oxidative stress and nitrative stress induced by Gentamicin in rats (El Gamal etal.,²⁰¹⁴). The similar protective effect with beetroot pretreatment was observed in rats with isoproterenol (ISP)‐induced myocardial injury (Raish etal.,²⁰¹⁹). Moreover, it was indicated that the presence of betanin contributed to the reduction of LDL in humans that reflected lipid peroxidation (Tesoriere etal.,²⁰⁰⁴). It was responsible for the postponement of cumOOH (cumene hydroperoxide)‐induced oxidization (Tesoriere etal.,²⁰⁰⁵). The application of beetroot was also proven useful for the mitigation of lipid membrane oxidation caused by the change of H₂O₂‐mediated metmyoglobin and free iron in vitro (Kanner etal.,²⁰⁰¹). The main antioxidant activity and related mechanisms described above were presented in Figure2a.

2.2. Antitumor activity

Cancer remains one of the leading causes of human death in the world. According to reports, there were 17.5 million cancer patients existing in 2015 (Javadi,²⁰¹⁸). At present, conventional interventions such as chemotherapy, surgery, and radiation are often used to help cancer patients get rid of the disease (Dennert & Horneber,²⁰⁰⁶). Although these interventions are available, the applications of which are also accompanied by some side effects (Dennert & Horneber,²⁰⁰⁶). For safety concerns, there is a great need to look for effective and safe methods for cancer treatment. The surveys elsewhere have indicated that the forms of some alternative and complementary medicine might actually stand a chance against cancer disease with less adverse effects (Bozza etal.,²⁰¹⁸; Trimborn etal.,²⁰¹³). In fact, beetroot just belongs to such medicine. The reports suggested that beetroot could act as a chemopreventive medicine with the capacity of reducing the formation of multi‐organ tumors and exhibiting less toxicity. Here, we reviewed the antitumor activity of the active component in beetroot and hoped that the application of beetroot would indeed become a feasible measure for future cancer treatment.

Prior to 1996, Govind J. Kapadia et al. began to study the antitumor activity of beetroot (Kapadia etal.,¹⁹⁹⁶). The results showed that the oral administration of betanin in beetroot contributed to the inhibition of skin and lung tumors in ICR mice pretreated with tumor promoter 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). Particularly in lung tumors, the reduction rate was up to 60%. It was the first report to illuminate the antitumor activity of beetroot using the animal model. With the development of research, the evidence emerging later also supports this finding. Govind J. Kapadia et al. once constructed three different tumor models in mice by using 7,12‐dimethylbenz(a)anthracene (DMBA), (±)‐(E)‐4‐methyl‐2‐[(E)‐hydroxyamino]‐5‐nitro‐6‐methoxy‐3‐hexanamide (NOR‐1) and TPA, N‐nitrosodiethylamine (DEN) and phenobarbital, respectively (Kapadia etal.,²⁰⁰³). During the experiment, they found that the betanin in beetroot significantly resisted the development of tumors caused by chemical carcinogens, suggesting that beetroot was a potent cancer chemopreventive agent. In addition, in HepG2 cells, treatment with beetroot component betanin resulted in the nuclear translocation of Nrf2 and then led to cell death (Krajka‐Kuźniak etal.,²⁰¹³). More importantly, betanin‐enriched beetroot had no obvious effect toward normal cells while the cytotoxicity of beetroot characterized on cancer cells was found powerful (Nowacki etal.,²⁰¹⁵). As the above results showed, beetroot was expected to be applied in the treatment of various tumors.

Up to now, researches have shown that inhibiting cell proliferation, promoting apoptosis, and autophagy are the main ways in which beetroot inhibits cancerous formation and development. For example, it was reported that beetroot (betalains and betaine) played a crucial role in reducing the number of esophageal papillomas induced by NMBA (N‐nitrosomethylbenzylamine) in rats (Lechner etal.,²⁰¹⁰). The exact mechanism involved was found to be associated with the inhibition of cell proliferation and stimulation of cell apoptosis, which was measured by immunohistochemical staining of Ki‐67 and terminal deoxynucleotidyl transferase dUTP nick end‐labeling staining. Besides, Laëtitia Nowacki et al. found that the application of betanin‐enriched extract was involved in the restriction of cancer cell viability (Trimborn etal.,²⁰¹³). The increase in the expression level of apoptosis‐related proteins (Bad, TRAILR4, FAS, p53) and alteration of the mitochondrial membrane potential was detected in MCF‐7 cells. Upon the beetroot treatment, it was also observed that autophagosome vesicles occurred in the MCF‐7 cells. In the study of other cells, the results existed likewise. The treatment of betanin separating from beetroot caused cleavage of procaspase‐3 and up‐regulation of ROS in CaCo‐2 cells (Zielińska‐Przyjemska etal.,²⁰¹⁶). Based on these results, we conclude that beetroot exerts cancer‐preventive activity by inducing cell apoptosis. However, as to whether there exists some correlation between ROS and apoptosis, it remains to be studied. Beetroot (Betanin) could also induce cell apoptosis by activating the expression of caspase‐3, caspase‐7, caspase‐9, and PARP in human lung cancer cell lines (Zhang etal.,²⁰¹³). In the study of rat model with CaCo‐2 cells, it was found that the combination of fermented beetroot juice (FBJ) and 2‐Amino‐1‐methyl‐6‐phenylimidazo[4,5‐b] pyridine (PhIP) abolished the cytotoxic and genotoxic effects induced by PhIP (Klewicka etal.,²⁰¹²). Compared with PhIP‐induced model, the group fed with PhIP and FBJ would effectively reduce the content of malondialdehyde and MDA in vivo. The antioxidant status of serum was also increased by 26% in the combined group, which suggested that the beetroot intake, mainly the betalains, was likely to enhance its anti‐oxygenic ability and provide protection against the formation of a precancerous aberrant crypt. In addition to the above pathways, studies have found that beetroot (betanin) could exert antitumor effects by inhibiting angiogenesis. The research of beetroot chemopreventive activity was conducted in two different animal lung tumor models (Zhang etal.,²⁰¹³). It was observed that the tumor multiplicity and load decreased in these two tumor models induced by Vinyl carbamate (VC)/benzo(a)pyrene (B(a)P) and beetroot. In the VC model, the tumor multiplicity and load were induced by 20% and 39%, respectively. In the model of B(a)P, the inhibition rate was up to 46% and 65%. Apart from the discovery of increased expression of caspase‐3, the number of CD31 in endothelial microvessels was found reduced after beetroot treatment, which suggested that cell apoptosis induction and angiogenesis inhibition were involved in the tumor inhibitory effects.

In addition to the above findings, the chemosensitization effects of beetroot in tumors also aroused great interest. Doxorubicin is an effective cytotoxic antitumor drug. It could be used clinically to treat various malignant tumor such as breast cancer, lung cancer, ovarian cancer, stomach cancer, and liver cancer (Cabeza etal.,²⁰¹⁷; Dag etal.,²⁰¹⁶; Marano etal.,²⁰¹⁷). However, the use of doxorubicin is often accompanied by some side effects, significantly limiting its clinical application (Dag etal.,²⁰¹⁶; Marano etal.,²⁰¹⁷). At present, doxorubicin is mainly used in combination with other antitumor drugs. Studies have found that the antitumor efficacy was also improved by the combination of beetroot and doxorubicin. For instance, Sayantanee. Das et al. once studied the effects of co‐treatment with beetroot and doxorubicin on breast cancer cells MDA‐MB‐231 (Das etal.,^{2013, 2016}). The results in this study showed that the ROS level and cell apoptosis both were increased with treatment of beetroot in MDA‐MB‐231 cells. Similarly, in the breast (MCF‐7), prostate (PC‐3), and pancreatic (PaCa) cells, the co‐administration of doxorubicin with beetroot exhibited synergistic effect (Kapadia etal.,²⁰¹³). Although Govind J. Kapadia et al. had previously declared that beetroot (betanin) exhibited significantly lower cytotoxicity compared with doxorubicin toward normal cells (Kapadia etal.,²⁰¹¹), it must continue to further explore the differential toxicity using doxorubicin alone or in combination with beetroot. Furthermore, the similar combined effects have been observed in studies using BC (Betacyanins) and XVX (Vitexin‐2‐O‐xyloside). A study by E. S. Scarpa et al. suggested that the combined use of XVX and BC caused an enhanced antitumor activity concerning the increased expression of pro‐apoptotic Bax, and downregulation of anti‐apoptotic BIRC5 (Survivin) and pro‐survival CTNNB1 (β‐Catenin) in T24 bladder cancer cells (Scarpa etal.,²⁰¹⁶). Unlike the previous research of doxorubicin and beetroot, it also pointed out the combination of XVX and BC had no cytotoxic effect toward normal cells NCTC 2544 (Scarpa etal.,²⁰¹⁶). However, it is not enough to use only one normal cell line to clarify their combination has less toxicity. It is necessary to offer toxicity assessment on other normal cells and carry out studies as supporting evidence in vivo. In another study, the scholars were not limited to research the combined effects of XVX and BC, betaxanthin (BX) that generated due to the resonance of double bond in BC was also involved (Farabegoli etal.,²⁰¹⁷). It was found that double combinations of XVX and BC, XVX and BX or triple combinations of XVX, BC and BX all caused an increase in cytotoxicity toward CaCo‐2 cells. This probably attributed to betalains for its ability to reduce the mRNA level of COX‐2 and IL‐8. For chronic lymphocytic leukemia (CLL) patients, it has begun to be gradually accepted that the application of beetroot–carrot juice provided a successful treatment for the complementary or alternative therapy combined with chlorambucil, a conventional leukemic treatment drug (Shakib etal.,²⁰¹⁵). This effect was proved by the decrease of the number of leukocytes, lymphocytes in peripheral blood and improve the relevant biochemical parameters.

Through all of the above (Figure2b), there is enough justification for the potential ability of beetroot used singly or combinedly for cancer treatment. However, due to the complexity of beetroot constituents, we cannot fully explain the contribution of a specific component to its antitumor activity yet. Some other components possibly also involved in minimizing the occurrence and stunting the development of cancer disease via other mechanisms. Perhaps, the different impacts of conventionally (CONV) and organically (ORG) produced beetroots on cancer cells were associated with these unknown compounds likewise (Kazimierczak etal.,²⁰¹⁴). For instance, betaine also was proved as an antitumor component in beetroot despite its activity being lower than betanin (Lee etal.,²⁰¹⁴). It was found that after exposure to betanin at a concentration of 200μg/ml, the inhibition rate on HepG2 cells was 49%, while it was just 25% inhibition rate achieved when the concentration of betaine reached 800μg/ml. Besides, because it is impossible to simulate the interaction between tumor and host by cell or animal experiments alone, the future research of beetroot should be more closely integrated with the human test model in vivo. Although beetroot rarely induces damage for its natural non‐toxic properties, it still needs to assess the probable interactions between beetroot and a conventional chemotherapy drug. It is guessed that the combined use with chemotherapy drug is likely to be the main aspect of future studies on the antitumor activity of beetroot.

2.3. Effect on blood lipids, glucose, and pressure

With the changes in current social living habits, diet, living environment, and other factors, hyperglycemia, high blood pressure, and high blood lipids have become nonnegligible chronic diseases that seriously threaten the human health (Anagnostis etal.,²⁰¹⁵; Christofaro etal.,²⁰¹⁴; Koskela etal.,²⁰¹³). It is reported beetroot possesses the ability to alleviate these diseases and has the advantages of no side effects compared with synthetic drugs. Therefore, an in‐depth study of active ingredients in beetroot and its related pharmacological function in chronic metabolic disease is of great significance.

It is reported that the function of lowering blood pressure by beetroot is associated with an ingredient isolated from beetroot that is dietary nitrate. Under the action of bacterial anaerobes situated on the tongue, the dietary nitrate would be activated into nitrite, thus exhibiting vasoprotective effects (Webb etal.,²⁰⁰⁸). The interruption of such conversion results in no obvious vasoprotective activity (Webb etal.,²⁰⁰⁸). Besides, in hypercholesterolemic patients, the alterations of oral microbiome would also influence the change from dietary nitrate to nitrite and therefore affects their vascular function (Velmurugan etal.,²⁰¹⁶). In chronic hypertension in pregnancy, it also speculated that the differences in efficacy of nitrate supplementation were related to differences in the oral microbiome (Ormesher etal.,²⁰¹⁸). In addition to having proven that the nitrate is the decisive form of beetroot to regulate the vascular function, the awareness of the impact of beetroot on microvascular vasodilation and arterial stiffness related to the vasoprotective effects is gradually increasing. Ditte A. Hobbs et al. found that the intake of nitrate in beetroot led to an increased curve area for endothelium independent vasodilation and decreased diastolic blood pressure (BP) in humans (Hobbs etal.,^{2012, 2013}). The results carried by Davi Vieira Teixeira da Silva's group indicated that the diastolic BP (5.2mmHg), systolic BP (6.2mmHg), and heart rate were decreased following the beetroot (nitrate) consumption in healthy subjects (Silva etal.,²⁰¹⁶). The reduction of BP also was enhanced with beetroot supplementation following a moderate‐intensity aerobic exercise in obese individuals (Lima Bezerra etal.,²⁰¹⁹). These findings have shown herein highlighted the testing of beetroot in vasoprotectiveness. Despite the above reports, the efficacy of beetroot in lowering blood pressure is affected by many other factors, such as age and sex (Coles & Clifton,²⁰¹²; Siervo etal.,²⁰¹⁵). The presence of Glu298Asp polymorphism in the endothelial NO synthase (eNOS) gene also affects the postprandial blood pressure response to dietary nitrate‐rich beetroot bread (Hobbs etal.,²⁰¹⁴). Recent research has raised different perspectives on the effects of beetroot diets on lowering blood pressure; that is, the consumption of raw beet juice (RBJ) and cooked beet (CB) has a difference in antihypertensive effects. The group of S. Asgary et al. once made a research and found that compared to CB, RBJ had a stronger antihypertensive effect in hypertensive subjects (Asgary etal.,²⁰¹⁶). While regarding the reason for the different effect between CB and RBJ, it requires to be further studied. Apart from the above findings, the key problem regarding the beetroot is to clarify the activity on treating hypertension, despite it is generally considered playing a role in lowering blood pressure. Research once pointed that the normalization of mRNA expression in CTGF, MCP‐1, and MMP‐2 followed by beetroot treatment would lead to the improvement of the hypertension in rat model, and this effect was induced by nitrate rather than betaine (Bhaswant etal.,²⁰¹⁷). Nevertheless, in the study of patients with hypertension, Bondonno et al. pointed out that there was no significant improvement of hypertension after beetroot intake (Bondonno etal.,²⁰¹⁵). C. P. Kerley et al. stated briefly that the function of beetroot in antihypertensive was achieved only among those patients with uncontrolled hypertension (Kerley etal.,²⁰¹⁷). The improvements in muscle microvascular function were also observed in never‐treated hypertensives (Zafeiridis etal.,²⁰¹⁹). In addition, research provided evidence that nitrate‐rich beetroot had an acute effect on circulating immune cells and platelets in older adults owing to decreased blood monocyte‐platelet aggregates and reduced blood CD11b‐expressing granulocytes (Raubenheimer etal.,²⁰¹⁷). In the subsequent study, therefore, the group determined to study whether the consumption of beetroot could reduce the risk of hypertension.

Hyperglycemia is another disease that the ingredients of betalains, polyphenols, and dietary nitrate in beetroot might have a great help for its treatment. It was found that with beetroot intake, the postprandial insulin response in the 0–60min phase and the glucose response in the phase of 0–30min were significantly downregulated in healthy volunteers (Wootton‐Beard etal.,²⁰¹⁴). A result shown in Biomedicine & Pharmacotherapy further supported for the standpoint that beetroot exhibited beneficial effects in maintaining glucose homeostasis. Dhananjayan Indumathi et al. constructed a diabetic rat model induced by streptozotocin (STZ, 40mg/kg b.w.) and nicotinamide (NA, 110mg/kg b.w.) (Dhananjayan etal.,²⁰¹⁷). After oral treatment with betanin, they found that followed by a significant increase of glycolytic enzyme (gluco*kinase and pyruvate kinase), glucose‐6‐phosphate dehydrogenase, and decrease in the activity of gluconeogenic enzymes (glucose‐6‐phosphatase and fructose‐1,6‐bisphosphatase), the levels of plasma glucose, insulin, glycosylated hemoglobin (HbA1c), and hemoglobin (Hb) were restored in diabetic rat. Unfortunately, however, because the current research on the anti‐hyperglycemia of beetroot is very limited, more research is urgently required.

Likewise, beetroot intake is benefit for hyperlipidemia treatment. The betalains in beetroot regulate peroxidation by scavenging lipid free radicals and then inhibiting peroxidase, nitrite‐induced oxidase, and human low‐density lipoprotein (Allegra etal.,²⁰⁰⁷). Wroblewska et al. revealed that the serum glucose levels, cecal atherosclerosis index, isovaleric acid concentration, and mice weight would significantly reduce in the hyperlipidemic model after feeding with beetroot (Sakihama etal.,²⁰¹²). The inhibition of short‐chain fatty acids and serum total sterols was also observed in beetroot‐treated mice due to the increase in excretion of bile acids (Sakihama etal.,²⁰¹²). Additionally, Zielinbska et al. carried an in vivo experiments with beetroot and found that following beetroot juice or beetroot slices intake, the oxidation metabolism of neutrophils was effectively inhibited in obese people, which thereby led to the reduction of body fat content (Wroblewska etal.,²⁰¹¹). These findings indicate that beetroot has potential application value for hyperlipidemia treatment.

From the above research (Figure3a) and the additional findings that nitrate in beetroot possesses the capacity of regulating flow‐mediated dilation (FMD) both in obese and normal‐weight people (Bakker etal.,²⁰¹⁵; Joris & Mensink,²⁰¹³), we believe that beetroot underlies the potential of a low cost and effective approach for the treatment of chronic disease including hyperglycemia and hyperlipidemia as well as the reduction of blood pressure. At present, it is necessary to conduct more research in a larger population to determine its applied range.

2.4. Improve exercise performance

The interest in various nutrients for improving athletic exercise performance has increased in recent years (Berry etal.,²⁰¹⁵). Due to the approved dietary nitrate on physical performance, nitrate‐rich beetroot thus attracts considerable attention. It is recognized that dietary nitrate decomposes into nitrite and subsequently converts to nitric oxide (NO) and other nitrogen‐active intermediates that affect the physical performance of athletic populations (Ferguson etal.,²⁰¹³). However, NO may lead to the formation of N‐nitroso compounds (NOCs) following a secondary pathway, making it be cautious with beetroot intake (Berends etal.,²⁰¹⁹). Up to now, many studies have been conducted on the impact of beetroot in the exercise performance of multifarious subjects.

In one study, for evaluating the possibility of supplementing beetroot juice to improve the athletic performance in short‐distance aerobic exercise, both the men and women athletes in national 500m kayak team were chosen as research objects (Peeling etal.,²⁰¹⁵). Peeling et al. then found that there were different increased degrees in exercise performance following the beetroot intake. However, it was found by Puype et al. that supplement with beetroot juice could not improve the athletic performance among these 22‐year‐old male volunteers under the intermittent hypoxic training condition (Puype etal.,²⁰¹⁵), which suggested that the nitrate in beetroot might only exert its effect under the aerobic condition. Under the condition of no oxygen or low oxygen, beetroot intake could not improve exercise performance and thereby lose the possibility of enhancing the endurance of anaerobic exercise. Apart from this, however, even under aerobic conditions, it was found that ingestion of beetroot supplementation did not work in all types of exercise. The acute ingestion of beetroot improved performance in a 30s Wingate test with increased peak power and shortened time to reach this maximum power in resistance trained athletes (Wickham etal.,²⁰¹⁹). However, it acted differently in recreational cyclists, national talent speed‐skaters, and Olympic‐level track cyclists that all were supplemented with 140ml/d nitrate‐rich and nitrate‐depleted beetroot juice, respectively. When these subjects have undergone two 6‐day intakes, three 30‐s Wingate tests were carried out immediately. The results then showed in the tests that there was no difference of peak power over the Wingates between the subjects treated with nitrate‐rich and nitrate‐depleted beetroot, while nitrate‐rich beetroot treatment responding to time to peak power over the Wingates was improved by ∼2.8% compared with nitrate‐depleted treatment (Jonvik, Nyakayiru, etal.,²⁰¹⁸). From these results, we speculate beetroot supplementation could enhance the capacity of accelerating during high‐intensity and sprint exercise. In the study of Lee J. Wylie et al., mean power output was found significantly increased in the nitrate‐rich group relative to the nitrate‐depleted group; however, such results could only present in high‐intensity intermittent exercise with the twenty four 6‐s all‐out sprints interspersed with 24s of recovery (Wylie etal.,²⁰¹⁶). The other evidence indicated that in severe‐intensity exercise, beetroot (nitrate) enhanced related exercise tolerance when the metabolic rate elevated (Breese etal.,²⁰¹³). During a perfusion pressure challenge, supplementation with nitrate‐rich beetroot made it possible for restoring its exercise capacity (Bentley etal.,²⁰¹⁷). Beetroot supplementation could also enhance the O₂ delivery and thus extend the working hours before fatigue begins (Lee etal.,²⁰¹⁵). In obese subjects, short‐term supplementation of beetroot could improve exercise tolerance (Rasica etal.,²⁰¹⁸). For hill‐walkers, acute 24‐hr supplementation of nitrate in beetroot also had important implications for such exercise (Waldron etal.,²⁰¹⁸). Even after blood donation, the intake of beetroot benefited to lower the cost of O₂ and attenuate the decline in exercise performance (McDonagh etal.,²⁰¹⁶). In spite of the above findings, there was no improvement in the exercise performance observed during the aerobic submaximal exercise despite nitric oxide increased following beetroot gel ingestion (Vasconcellos etal.,²⁰¹⁷). Combination of beetroot (nitrate) and caffeine exhibited no obvious effect in athletic performance during submaximal or maximal treadmill running exercise (Oskarsson & McGawley,²⁰¹⁸). Even for intermittent exercise, ingesting nitrate in beetroot did not improve the performance of elite female athletes (Jonvik, van Dijk, etal.,²⁰¹⁸). For moderately trained swimmers, it did not work at least for 100‐m and 200‐m freestyle swimming performance with beetroot intake (Esen etal.,²⁰¹⁹). Thus, it is guessed that many factors involved in the limitation of beetroot‐induced effects.

At present, many studies are currently working on the inherent mechanisms by which beetroot enhances exercise performance. However, the insight on the relevant mechanism remains to be disputable, and all of the possible mechanisms described below are shown in Figure3b. Roger A. Vaughan et al. held the point that nitrate‐containing beetroot extract was acted as an inducer to regulate the metabolic gene expression and mitochondrial content (Vaughan etal.,²⁰¹⁵). Along with the up‐regulated oxidative metabolism, the expression of metabolic genes such as mitochondrial transcription factor A and peroxisome proliferator‐activated receptor gamma coactivator‐1 alpha was also elevated in C2C12 cells (Vaughan etal.,²⁰¹⁵). In addition, during fatiguing resistance exercise for fourteen men, supplementation with beetroot‐based supplements could cause a neuromuscular advantage, that is, enhancing the neuromuscular efficiency (Flanagan etal.,²⁰¹⁶). In the study of Scott Betteridge et al., however, they found that there was no significant decrease in muscle glycogen, phosphocreatine and increase in phosphorylated acetyl CoA carboxylase, muscle creatine and lactate with nitrate‐rich beetroot intake in males (Betteridge etal.,²⁰¹⁶). A result revealed by J. Whitfield et al. that even under the action of beetroot, there existed no change in uncoupling proteins (UCP3, ANT1, ANT2), ADP sensitivity, P/O ratio, respiratory control ratios, and membrane potential. Therefore, the mitochondrial efficiency was found unaltered following beetroot supplementation in humans (Whitfield etal.,²⁰¹⁵). As the results indicated the H₂O₂ emission increased after beetroot intake (Whitfield etal.,²⁰¹⁵), it still required further study.

Along with possible effects on athletic performance, supplementation with beetroot was also likely to attenuate muscle soreness. Tom Clifford et al. found that when the level of pressure pain threshold (PPT) in a high and low dose of beetroot‐treated groups had returned to baseline at 72hr postexercise, the level of which was still decreased in the placebo‐treated group (Clifford etal.,²⁰¹⁶). In the subsequent study, they clarified that the phytonutrients in beetroot or the interaction between phytonutrients and nitrate might contribute to such effect (Clifford, Howatson, etal.,²⁰¹⁷). Additionally, the benefits of beetroot were confirmed by the evidence that the beetroot did not adversely affect the body during exercise (Clifford, Bell, etal.,²⁰¹⁷; Murphy etal.,²⁰¹²). Due to these protective effects and enhanced performance activity, sports drinks based on beetroot are receiving increasing attention. For instance, Vanajakshi et al. made full use of lactobacillus to ferment beetroot and moringa to make a drink (Vanajakshi etal.,²⁰¹⁵). A sports drink composed of beetroot extract, creatine, sulfuric acid, and calcium 3‐hydroxy‐3‐methylbutyrate was found to possess the capacity of increasing muscle blood flow, improving oxygen utilization, reducing exercise energy consumption, and thus to improve exercise performance. The application of beetroot products will be the research hotspot in the future.

2.5. Other activities

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