2021 Volume 27 Issue 5 Pages 807-816
Insect feces tea has been used as traditional Chinese medicine. Obesity is one of the main factors of lifestyle diseases, so prevention and improvement of obesity are indispensable for living a healthy life in modern society. We examined the lipid accumulation-suppressing effect of tea from Locusta migratoria (LT) in vitro and in vivo assays. LT suppressed the differentiation of 3T3-L1 cells to adipocytes, but not the process of accumulation of lipid droplets. Furthermore, it suppressed the expression of peroxisome proliferator-activated receptor (PPAR)γ and CCAAT/enhancer-binding protein (C/EBP)α, master regulators of differentiation. In mice fed a high-fat diet and administered with LT, the body weight did not change compared to the mice fed with water; however, the white fat weight, particularly the visceral fat, was reduced significantly. These results indicated the potential of LT to suppress fat accumulation by inhibiting adipocyte differentiation.
It has been speculated that the human population on Earth will reach 10 billion in 2070 and that the temperature will rise by 7.5 °C from the current temperature due to excessive global warming (Fedoroff, 2015; Xu et al., 2020). Consequently, a serious food crisis is predicted to occur worldwide because there will not be enough food for the entire human population. In 2013, the Food and Agriculture Organization of the United Nations proposed the active use of insects as food and feed (van Huis et al., 2013). Furthermore, the European Union began to regulate insects as a novel food in 2015. In other words, insects, which have been used as common foods in Asia and Africa, joined the food category in Europe, where insect-eating was not a habit. One of the main reasons for the inclusion of insects as food is attributed to their high nutritional value comparable to that of animal meats, including cattle, pigs, and chickens. Insects contain high levels of protein, as well as large amounts of lipids, beneficial fatty acids, vitamins, and minerals (Kim et al., 2019; de Castro et al., 2018; Ghosh et al., 2017). In Southeast Asia, particularly in Thailand and Laos, the farming of lepidopteran insects has already been put into practical use, and in Japan, research on the farming of crickets and locusts has begun. It is believed that insect farming will spread and progress worldwide in the near future.
The feces of insects have been consumed as insect tea in China since ancient times. Insect tea is prepared from the feces of the moth larvae fed with naturally fermented and finely crushed leaves, which undergo a further step of fermentation by the internal enzymes of the larvae. Insect tea has not only a very good taste and flavor but also contains various ingredients, such as amino acids, minerals, fatty acids, and volatile oils. In addition, insect tea contains many antioxidants, including polyphenols (Xu et al., 2013). This tea is considered to have antioxidant activity that can eliminate free radicals in the body as well as anti-inflammatory effects (Zhao et al., 2018). Additionally, several functionalities of insect tea have also been reported. For instance, Sanye insect tea has been shown to have a hypoglycemic effect, whereas Hawk insect tea has been reported to have serum TC, TG, and low-density lipoprotein cholesterol-reducing effects (Xu et al., 2013), indicating the possible anti-diabetic and anti-obesity effects of insect tea. It is assumed that there will be an increase in the number of areas in which the cultivation of edible insects will increase with the spread of insect food consumption. As a consequence, it is expected that the amount of insect feces discharged by the farmed insects will increase and become a waste burden. Therefore, using feces to prepare insect tea, which has high functionality and health benefits similar to commonly used teas, such as green tea and black tea, could practically be helpful.
As obesity is the cause of lifestyle diseases, the prevention and improvement of obesity are indispensable for living a healthy life in modern society. In particular, an increase in visceral fat can cause metabolic syndromes in which dyslipidemia, hyperglycemia, and hypertension are triggered by visceral fat obesity (Reaven, 2006). Patients with metabolic syndrome have been reported to be about three times more likely to develop type 2 diabetes or die from cardiovascular disease than those who do not (Ford, 2005). Obesity is attributed to the increase in adipocyte counts and hypertrophy. Recent investigations have demonstrated that peroxisome PPARγ, C/EBPα and β, and sterol regulatory element-binding transcription factor 1 are transcription factors that regulate adipocytes differentiation (de sá et al., 2017). Adipocytes differentiate via the PPARγ and C/EBPα pathway (Rosen et al., 2002). Therefore, it is important to inhibit these transcription factors to suppress the differentiation of adipocytes. Functional foods and ingredients have garnered attention as a means to maintain health. Indeed, many foods have been reported to have fat accumulation-suppressing effects (Hasumura et al., 2012; Suk et al., 2016; Neil et al., 2019). However, the fat accumulation-suppressing effects of insect feces tea have not yet been reported. In this study, we investigated the use of insect feces of Locusta migratoria as a tea and examined its lipid accumulation-suppressing effect.
Extraction from feces of L. migratoria The feces of L. migratoria bred with wheat (Bromus catharticus) at 30 °C in the National Institute of Agrobiological Sciences (Ibaraki, Japan) were used. Feces were collected as appropriate during breeding. Feces tea of L. migratoria (1 g) was extracted using boiled water (50 mL) for 10 min. The solution of the feces of L. migratoria extracted with boiled water was centrifuged at 10 000 × g for 10 min and filtered through a 0.45-µm-pore filter membrane. The filtrate (∼20 mg feces/mL) was used as LT. The test solutions with 0.25, 0.5 and 1.0 mg feces/mL were prepared by diluting LT with assay medium and used for in vitro assays using 3T3-L1 cells.
Cell culture and differentiation 3T3-L1 cells were obtained from the American Type Culture Collection (ATCC; Manassas, VA, USA) and cultured in Dulbecco's modified Eagle's medium (DMEM; Sigma-Aldrich, St. Louis, MO, USA) supplemented with 10% fetal calf serum (Gibco, Thermo Fisher Scientific, Waltham, MA, USA), 100 U/mL penicillin, and 100 U/mL streptomycin (Sigma-Aldrich) as the growth medium at 37 °C under 5% CO2. Penicillin and streptomycin were added to all of the culture media used thereafter. Briefly, cells were seeded at 5.0 × 104 cells per well in 24-well plates and cultured in growth medium until 100% confluent for 4 d (period 1). The medium was changed to a differentiation medium (DMEM supplemented with 10% fetal bovine serum (Gibco, Thermo Fisher Scientific), isobutylmethylxanthine, dexamethasone, and insulin (Adipogenesis Assay Kit, Cayman Chemical, MI, USA)) to induce differentiation for 3 d (period 2). After 3 d, the medium was replaced with a maintenance medium (DMEM supplemented with 10% fetal bovine serum), and the cells were cultured for 4 d (period 3). Three tests were performed: in Test I, LT was added to the medium in both periods 2 and 3; in Test II, LT was added only in period 2; and in Test III, LT was added only in period 3. Cells not treated with LT were used as the control. The cytotoxicity of LT on 3T3-L1 cells was examined in Test I with Cell Counting Kit-8 (Dojindo Laboratories, Kumamoto, Japan).
Oil Red O staining Intercellular lipid accumulation was measured by Oil Red O staining. 3T3-L1 cells on a 24-well plate were incubated in a differentiation medium (500 µL) with or without LT. The final concentration of LT was 0.25, 0.5, and 1.0 mg/mL. After 3 d of incubation, the medium was replaced with a maintenance medium (500 µL) with or without LT. After 4 d of incubation, cells were washed twice with phosphate-buffered saline and fixed in a 10% formalin (Nacalai Tesque, Osaka, Japan). The fixed cells were washed twice with water, then stained by 0.3% Oil Red O for 15 min at room temperature. After discarding the solution, the stained droplets in the cells were washed three times with water. The droplets were extracted from the cells with isopropanol for 20 min at room temperature, then the absorbance of the extracts was measured at 520 nm (Ramírez-Zacarías et al., 1992). Results are shown as the relative percentage of differentiated cells in comparison to the control cells without LT.
mRNA preparation and real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) 3T3-L1 cells on a 24-well plate were incubated in differentiation medium (500 µL) containing LT (0.25, 0.5, or 1.0 mg/mL). After the induction of differentiation, the cells were harvested every day for 3 days, and total RNA was extracted from the cells using an RNeasy Kit (Qiagen N.V., Venlo, Netherlands) according to the manufacturer's instructions. cDNA was synthesized using random primers and PrimeScript Reverse Transcriptase (Takara Bio, Shiga, Japan). An aliquot of cDNA was used as a template for qRT-PCR in a StepOnePlus Real-Time PCR System (Applied Biosystems, Foster City, CA, USA). The target cDNAs were amplified using Fast SYBR Green Master Mix (Applied Biosystems) together with the following gene-specific primers: PPARγ (MA029808; Takara Bio), C/EBPα (MA024950; Takara Bio), and βACTIN (MA050368; Takara Bio). The relative expression level of each mRNA was normalized to the expression of the housekeeping gene βACTIN.
Animal treatments Four-week-old male C57BL/6NCrSlc mice were obtained from Japan SLC, Inc. (Shizuoka, Japan). The mice were preliminarily bred for 3 days as the acclimatization period. For the entire study, including the preliminary breeding period, the mice were bred in an environment with a 12-h light-dark cycle and free access to food and water. During the preliminary breeding period, all mice were kept in cages with six mice per cage and were fed the solid diet CLEA Rodent Diet CE-2 (CLEA Japan, Tokyo, Japan) as a normal diet. After the preliminary breeding period, all mice were weighed and assigned to one of three weight-matched groups—the first group was fed a normal diet (ND) with water (n = 4), the second group was fed a high-fat diet (HFD) with water (n = 5), and the third group was fed an HFD with LT (n = 6) for 11 weeks. As the high-fat feed, HFD-60 (Oriental Yeast, Tokyo, Japan) was used. The concentration of LT was 8 g/400 mL. After 11 weeks of dietary treatment, blood was collected from the abdominal vena cava of the group fed an ND with water (n = 4), and the groups fed an HFD with water (n = 3) or LT (n = 6). Liver and adipose tissues (epididymal fat, perirenal fat, inguinal fat, and interscapular fat) were collected from the group fed an ND with water (n = 4), the groups fed an HFD with water (n = 5) or LT (n = 6). After collection, they were weighed, frozen in liquid nitrogen, and stored at −80 °C. The experimental protocol for this study was approved by the Animal Care and Use Committee at Yamaguchi University (number 276), accredited by AAALAC International.
Measurement of blood and liver components The plasma was obtained by centrifuging blood at 600 × g and 4 °C for 10 min. The liver fragment was weighed in a tube, homogenized in a mixed solution of methanol: chloroform (1:2), then extracted by sonication. After centrifugation at 16 000 × g and 4 °C for 10 min, the solvent was collected into a new tube, phosphate-buffered saline was added and mixed with a vortex mixer. After centrifugation at 16 000 × g and 4 °C for 10 min, the chloroform layer was recovered. Subsequently, the solvent was volatilized at 4 °C and redissolved in isopropanol and was used as the sample. For TG measurement, free fatty acid, TC, and blood sugar levels, Lab Assay™ Triglyceride, Lab Assay™ NEFA, Lab Assay™ Cholesterol, and Lab Assay™ Glucose (Wako Pure Chemical, Osaka, Japan) were used.
Statistical analyses Data were analyzed using one-way analysis of variance followed by Dunnett's test or Tukey test using GraphPad Prism (GraphPad Software, San Diego, CA, USA). Statistical significance was denoted by values of p < 0.01 or p < 0.05.
Suppressing effect of LT on lipid accumulation in 3T3-L1 cells First, to examine whether LT has a lipid accumulation-suppressing effect. For this purpose, 3T3-L1 cells to which LT was added (0.25, 0.5, or 1.0 mg/mL) were subjected to Oil Red O staining (Fig. 1A). LT attenuated the Oil Red O staining level in a concentration-dependent manner and suppressed more than 75% of the staining at all concentrations tested (Fig. 1B). Therefore, it was confirmed that LT had a lipid accumulation-suppressing effect. Next, to investigate the mechanism by which LT suppresses cell differentiation, LT was added to the cells in the experimental scheme shown in Figure 2A, and Oil Red O staining was performed (Fig. 2B). The staining level of cells in Test III was the same as that in the control cells, i.e., LT did not suppress lipid accumulation when added only in period 3. In contrast, cells in Tests I and II showed almost the same staining level, and their level was less than that in the control cells (Fig. 2C). These results indicated that LT suppressed lipid accumulation during the process of 3T3-L1 differentiation into adipocytes but not during the process of lipid droplet accumulation. The viability of 3T3-L1 cells treated with LT was also measured. LT showed no toxicity during the experimental process at concentrations below 1.0 mg/mL (data not shown).
Effect of insect tea of Locusta migratoria (LT) on adipocyte differentiation in 3T3-L1 cells.
(A) Representative images of Oil Red O staining. Adipogenesis was induced in the presence or absence of LT (0, 0.25, 0.5, or 1.0 mg/mL LT). (B) The droplets were extracted from the cells with isopropanol. Then, the absorbance of the extracts was measured at 520 nm. Results are shown as the relative percentage of the control values. Values are expressed as the mean ± standard error of the mean (n = 3). **p < 0.01 when compared to the control.
The inhibitory effect of insect tea of Locusta migratoria (LT) occurred during the first stage of adipogenesis.
(A) The scheme of the investigation. Intracellular lipid accumulation was assessed by staining with Oil Red O solution. In Test I, LT was added to the medium in both periods 2 and 3; in Test II, LT was added only in period 2; and in Test III, LT was added only in period 3. The concentration of LT added was 1.0 mg/mL. (B) Representative images of Oil Red O staining. (C) The droplets were extracted from the cells with isopropanol. Then, the absorbance of the extracts was measured at 520 nm. Results are shown as the relative percentage of the control values. Values are expressed as the mean ± standard error of the mean (n = 3). **p < 0.01 when compared to the control.
Effect of LT on the gene expression of PPARγ and C/EBPα in 3T3-L1 cells Because PPARγ and C/EBPα are the master regulators of adipocyte differentiation in 3T3-L1 cells, the expression of these genes was examined by qRT-PCR in cells during period 2 (incubation in differentiation medium; Fig. 2A). LT did not suppress the expression of PPARγ on the 1st day after the induction of differentiation, but after 2 days, it significantly suppressed the expression of PPARγ in a concentration-dependent manner compared to the control cells not treated with LT (Fig. 3). In contrast, LT significantly suppressed the expression of C/EBPα from the 1st day of differentiation induction, and the suppression became stronger with each passing day (Fig. 3).
Effect of insect tea of Locusta migratoria (LT) on the expression of PPARγ and C/EBPα in 3T3-L1 cells.
The expression of PPARγ and C/EBPα was examined by real-time quantitative reverse transcription-polymerase chain reaction every day during the 3 days of period 2. Values are expressed as the mean ± standard error of the mean (n = 3). **p < 0.01 when compared to the value of the control on day 1.
Effect of LT on the body weight and white adipose tissue (WAT) of mice fed a high-fat diet Following 11 weeks of breeding, the body weight of mice fed an HFD was higher than those of mice fed an ND, whereas there was no difference in between the group fed an HFD with water and that with LT (Figure 4A). Additionally, the feed intake of the mice fed an HFD with water was 2.91 ± 0.15 g/d mouse and that with LT was 2.88 ± 0.11 g/d/mouse, which was almost same. Furthermore, all WAT weights were higher in mice fed an HFD than in mice fed an ND (Fig. 4B). The epididymal WAT weight was significantly lower in the group fed an HFD with LT than that with water. There was no significant difference in other adipose tissues, but it tended to decrease in the group fed an HFD with LT (Figure 4B). When the epididymal WAT and perirenal WAT were considered to constitute the visceral WAT, and the inguinal WAT and interscapular WAT were considered to constitute the subcutaneous WAT, the visceral WAT in the LT-treated mice group was significantly decreased (Fig. 4C). Furthermore, the total WAT weight was significantly lower in the group fed an HFD with LT than that with water (Fig. 4C). These results showed that LT suppressed the accumulation of fat induced by the HFD.
Effect of insect tea of Locusta migratoria (LT) on the body weight of mice and white adipose tissue (WAT)
(A) Effect of LT on the body weight in male C57BL/6NCrSlc mice fed a normal diet with water (ND + water; n = 4), a high-fat diet with water (HFD + water; n = 5) or LT (HFD + LT; n = 6) at the end of the experimental period. (B) Effect of LT on the weights of WAT in C57BL/6NCrSlc mice at the end of the experimental period. (C) The epididymal WAT and perirenal WAT were considered to constitute the visceral WAT, and the total inguinal WAT and interscapular WAT were considered to constitute the subcutaneous WAT. The sum of all WAT masses was taken to be the total WAT mass. Values are expressed as the mean ± standard error of the mean. Data were analyzed by one-way ANOVA with Tukey test; *p < 0.05 and **p < 0.01.
Effect of LT on blood and liver components in mice fed a high-fat diet TG, free fatty acid, TC, and glucose levels were measured in the collected plasma. TC and glucose increased when mice were fed an HFD (Fig. 5A). In addition, TC in mice fed an HFD with LT tended to decrease with respect to that with water (P = 0.078). Furthermore, there were no significant changes in free fatty acids and TG content among the three groups (Fig. 5A). TC and TG levels were measured in the collected liver. TC and TG increased when mice were fed an HFD (Fig. 5B). TC was significantly higher in the group fed an HFD with LT than that with water, and TG did not decrease in the group fed an HFD with LT (Fig. 5B).
Effect of insect tea of Locusta migratoria (LT) on plasma and liver components.
(A) Effect of LT on the cholesterol, glucose, free fatty acid, and triglyceride levels of plasma in male C57BL/6NCrSlc mice fed a normal diet with water (ND + water; n = 4), a high-fat diet with water (HFD + water; n = 3) or LT (HFD + LT; n = 6) at the end of the experimental period. (B) Effect of LT on the cholesterol and triglyceride levels of the liver in male C57BL/6NCrSlc mice fed a normal diet with water (ND + water; n = 4), a high-fat diet with water (HFD + water; n = 5) or LT (HFD + LT; n = 6) at the end of the experimental period. Values are expressed as the mean ± standard error of the mean. Data were analyzed by one-way ANOVA with Tukey test; *p < 0.05 and **p < 0.01.
Although there are varying opinions on the diagnostic criteria for obesity (Reaven, 2006; Elabbassi and Haddad, 2005), obesity has been considered a risk factor for diseases, such as diabetes, hypertension, and arteriosclerosis, since the World Health Organization announced the term “metabolic syndrome” in 1998. Recently, metabolic syndrome in children, especially in developed countries, has become recognized as a problem because poor eating habits during childhood can become a cause of diabetes in adults (Al-Hamad & Raman, 2017). Metabolic syndrome has become a serious problem in all generations, and there is an urgent need to control and eliminate obesity. In this study, we investigated the lipid accumulation-suppressing effect of LT both in vitro and in vivo as the consumption of insect tea represents a method of waste utilization from insect cultivation, which will increase with the expected spread of insect food.
The differentiation of cells into adipocytes and the accumulation of lipid droplets are considered to be the cellular mechanisms that lead to obesity. In this study, we found that LT suppressed PPARγ and C/EBPα, which are master regulators of differentiation. Various studies have reported that the mechanism of action that suppresses PPARγ differs depending on the food. It is known that ginger, coffee, and green tea are typical foods that have an anti-obesity effect. Ginger suppresses the accumulation of lipid droplets by mainly suppressing the expression of fatty acid synthase and acetyl CoA carboxylase (Wang et al., 2017). In other words, ginger is an example of a food that can suppress the accumulation of fat during period 3 of this experiment. However, as was seen with LT in the present study, coffee and green tea have also been reported to suppress the differentiation of progenitor cells into adipocytes (Raseetha et al., 2017; Lin et al., 2005; Aoyagi et al., 2014; Maki et al., 2017). Coffee suppresses adipocyte differentiation by suppressing PPARγ in 3T3-L1 cells (Aoyagi et al., 2014). It has also been reported that coffee suppresses obesity by suppressing the expression of insulin receptor substrate 1 (IRS1), an insulin receptor adapter protein located upstream of PPARγ and C/EBPα (Maki et al., 2017). The active ingredient of coffee is considered to be the ingredient of roasted coffee beans and has not yet been specified. Tea catechin, one of the main active ingredients of green tea, has been reported to suppress PPARγ and C/EBPα in 3T3-L1 cells (Suzuki et al., 2016). 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR), which is an AMP-activated protein kinase (AMPK) activator, has been shown to suppress the expression of PPARγ and C/EBPα in 3T3-L1 cells, suggesting that these transcription factors are regulated by AMPK (Habinowski and Witters, 2001). In addition, it has been reported that obesity was suppressed in a group of mice administered a green tea extract because AMPK was mainly induced in adipose tissue, and the expression of PPARγ was suppressed (Rocha et al., 2016). In this experiment, B. catharticus was used as feed in the breeding of locust, and the active ingredient was considered to be derived from B. catharticus or the locust itself. Some studies have shown that saponarin, a flavonoid present in barley belonging to the same family as B. catharticus, suppresses lipid accumulation (Lee et al., 2015; Kim et al., 2017). In a previous study, saponarin suppressed fat accumulation in mice via AMPK activation (Kim et al., 2017). Saponarin was also reported to suppress fat accumulation in 3T3-L1 cells (J. S. Kim et al., 2020). It was highly possible that saponarin suppressed the expression of PPARγ by activating AMPK. Through these published results, it was considered that LT contained B. catharticus-derived polyphenols like saponarin, which activated AMPK and suppressed PPARγ, thereby suppressing fat accumulation.
Based on the findings of the in vitro experiments that demonstrated the fat accumulation-suppressing effect of LT, an in vivo experiment was performed by administering LT to mice, and the same effect was verified in the mice. The findings revealed that visceral WAT was significantly reduced by LT treatment. Though visceral WAT and subcutaneous WAT are both white fat, their properties differ—Subcutaneous WAT has a high ability to synthesize and accumulate fat, while visceral WAT synthesizes and secretes adipocytokines that control sugar and lipid levels in the blood as well as the blood pressure (Dutheil et al., 2018). The accumulation of visceral WAT causes the abnormal secretion of these adipocytokines, leading to the development of various diseases (Kaisanlahti and Glumoff, 2019). For example, after decomposition, the accumulated fat can reenter the circulatory system, leading to increased cholesterol and TG levels in the blood, which can cause arteriosclerosis. Alternatively, the secretion of tumor necrosis factor α, which blocks the function of insulin, is increased, leading to insulin resistance and contributing to diabetes. When these symptoms occur, it leads to metabolic syndrome. Although not at a statistically significant level, LT tended to decrease the blood TC. It was considered that the reason why the blood TG tended to decrease in this experiment was that the visceral fat decreased. These results suggested that LT has the possibility to improve metabolic syndrome.
A study comparing the polyphenols of Kuding tea and insect feces tea prepared from the insects fed with the Kuding tea leaves has demonstrated that polyphenol from insect feces tea increased the activity of superoxide dismutase, glutathione peroxidase and glutathione, and reduced activity of nitric oxide and malonaldehyde in mice than polyphenols in Kuding tea (Zhao et al., 2018). Although these polyphenols were not identified, it was predicted that the transformation of Kuding tea polyphenols in insects could have increased the antioxidant activity in the latter. Several studies have shown that plant polyphenols act as defensive agents against insects (Orozco-Cardenas et al., 1993) (Chung et al., 2013). Reportedly, polyphenols act as digestive inhibitors for insects, hence insects neutralize the action of polyphenols by secreting glycine in the body. Briefly, upon feeding, polyphenols are oxidized and converted to quinones that bind to proteins to form macromolecules, consequently making protein nonnutritive (Konno et al., 1997). To avoid this, insects use glycine that prevents the binding of quinones to proteins. Additionally, it has been shown that quinones have high reactivity and can transform into other polyphenols (Masuda et al., 2005). For instance, purpurin, a quinone, has been shown to have the ability to suppress lipid accumulation (Nam et al., 2019).
Moreover, insect feces are fermented by gut bacteria as they pass through the digestive system of the insect (Dillon and Dillon, 2004). It has been reported that the flavonoids, epigallocatechin and gallocatechin, are converted by gut bacteria, Adlercreutzia equolifaciens JCM 14793, Asaccharobacter celatus JCM 14811, Slackia equolifaciens JCM 16059 and Slackia isoflavoniconvertens JCM 1613712, that metabolize isoflavones (Takagaki and Nanjo, 2015). Similarly, daidzein, a soy isoflavone, is metabolized to equol, which has stronger estrogenic activity, by the lactic acid bacterium, Lactococcus garvieae (Mayo et al., 2019; Shimada et al., 2012). Collectively, these studies indicate that the polyphenols in plants upon feeding are converted into other active ingredients in insects, which is passed into their feces; thereby increasing the functionalities of the latter. There are no reports on the components of B. catharticus and their ability to suppress lipid accumulation. However, these facts suggest that LT might have the polyphenols derived from B. catharticus, which could have gained higher functionalities being modified by locust gut microbiota.
In the past, insect food was looked down upon and was generally not eaten, except in a few areas. However, insects are now recognized as food globally, which may help solve food shortage problems in the future. In fact, insects can be nutritious as food. Furthermore, the use of insect food may have environmental benefits. Since ancient times, insect tea has been used as an herbal medicine in parts of China, and it is said to have various beneficial effects. In this study, we demonstrate one of its efficacies and show the potential of insect food as a functional food. We hope that research on the functionality of various insects will progress in the future and that insect food will be used as a functional food that can relieve adult diseases as well as food shortages.
Acknowledgements We are grateful to Dr. Seiji Tanaka for advice on breeding locusts at the National Institute of Agrobiological Sciences. This work was supported partly by the Japan Society for the Promotion of Science Grant numbers 26660113 to Yoshihito Iuchi.
Conflict of interest There are no conflicts of interest to declare.
Locusta migratoria
TCTotal cholesterol
TGTriglyceride
PPARγPeroxisome proliferator-activated receptor γ
C/EBPαCCAAT/enhancer-binding protein α
