Physiologic hormone administration improves HbA1C in Native Americans with type 2 diabetes: A retrospective study and review of insulin secretion and action.

Insulin is secreted in pulses from pancreatic beta-cells, and these oscillations maintain fasting plasma glucose levels within a narrow normal range. Within islets, beta-cells exhibit tight synchronization of regular oscillations. This control circuit is disrupted in type 2 diabetes, and irregularities in pulse frequency and amplitude occur. The prevalence of type 2 diabetes is three times higher in American Indian and Native Alaskans compared to Whites, and their genetic ancestry is associated with low beta-cell function. Obesity in this population compounds their vulnerability to adverse outcomes. The purpose of this article is to review insulin secretion and action and its interaction with race. We also present the results from a 6-month retrospective chart review of metabolic outcomes following intravenous physiologic hormone administration to 10 Native Americans. We found reductions in hemoglobin A1C (baseline: 9.03% ± 2.08%, 6 months: 7.03% ± 0.73%, p = 0.008), fasting glucose (baseline: 176.0 ± 42.85 mg/dL, 6 months: 137.11 ± 17.05 mg/dL, p = 0.02), homeostatic model assessment of insulin resistance (baseline: 10.39 ± 4.66, 6 months: 7.74 ± 4.22, p = 0.008), and triglycerides (baseline: 212.20 ± 101.44, 6 months: 165.50 ± 76.48 mg/dL, p = 0.02). Physiologic hormone administration may improve components of the metabolic syndrome. The therapy warrants investigation in randomized controlled trials.

Naringenin and ß-carotene convert human white adipocytes to a beige phenotype and elevate hormone- stimulated lipolysis.

Introduction: Naringenin, a peroxisome proliferator-activated receptor (PPAR) activator found in citrus fruits, upregulates markers of thermogenesis and insulin sensitivity in human adipose tissue. Our pharmacokinetics clinical trial demonstrated that naringenin is safe and bioavailable, and our case report showed that naringenin causes weight loss and improves insulin sensitivity. PPARs form heterodimers with retinoic-X-receptors (RXRs) at promoter elements of target genes. Retinoic acid is an RXR ligand metabolized from dietary carotenoids. The carotenoid ß-carotene reduces adiposity and insulin resistance in clinical trials. Our goal was to examine if carotenoids strengthen the beneficial effects of naringenin on human adipocyte metabolism. Methods: Human preadipocytes from donors with obesity were differentiated in culture and treated with 8µM naringenin + 2µM ß-carotene (NRBC) for seven days. Candidate genes involved in thermogenesis and glucose metabolism were measured as well as hormone-stimulated lipolysis. Results: We found that ß-carotene acts synergistically with naringenin to boost UCP1 and glucose metabolism genes including GLUT4 and adiponectin, compared to naringenin alone. Protein levels of PPARα, PPARγ and PPARγ-coactivator-1α, key modulators of thermogenesis and insulin sensitivity, were also upregulated after treatment with NRBC. Transcriptome sequencing was conducted and the bioinformatics analyses of the data revealed that NRBC induced enzymes for several non-UCP1 pathways for energy expenditure including triglyceride cycling, creatine kinases, and Peptidase M20 Domain Containing 1 (PM20D1). A comprehensive analysis of changes in receptor expression showed that NRBC upregulated eight receptors that have been linked to lipolysis or thermogenesis including the ß1-adrenergic receptor and the parathyroid hormone receptor. NRBC increased levels of triglyceride lipases and agonist-stimulated lipolysis in adipocytes. We observed that expression of RXRγ, an isoform of unknown function, was induced ten-fold after treatment with NRBC. We show that RXRγ is a coactivator bound to the immunoprecipitated PPARγ protein complex from white and beige human adipocytes. Discussion: There is a need for obesity treatments that can be administered long-term without side effects. NRBC increases the abundance and lipolytic response of multiple receptors for hormones released after exercise and cold exposure. Lipolysis provides the fuel for thermogenesis, and these observations suggest that NRBC has therapeutic potential.

Safety and Tolerability of Whole Soybean Products: A Dose-Escalating Clinical Trial in Older Adults with Obesity.

Soybean products have nutrients, dietary fiber, and phytoalexins beneficial for cardiovascular and overall health. Despite their high consumption in Asian populations, their safety in Western diets is debated. We conducted a dose-escalating clinical trial of the safety and tolerability of soybean products in eight older adults (70-85 years) with obesity. Whole green soybean pods grown under controlled conditions were processed to flour (WGS) at the United States Department of Agriculture using common cooking techniques such as slicing and heat treatment. WGS incorporated into food products was consumed at 10 g, 20 g, and 30 g/day for one week at each dose. The gastrointestinal outcomes, clinical biomarkers, and adverse events were evaluated. We explored the stimulation of phytoalexin (glyceollin) production in live viable soybean seeds (LSS-G). We compared the compositions of WGS and LSS-G with commercial soybean flour and its fermented and enzymatically hydrolyzed forms. We found that although 30 g WSG was well-tolerated, and it made participants feel full. Our processing produced glyceollins (267 µg/g) in LSS-G. Processing soybean flour decreased the iron content, but reduced the oligosaccharides, which could attenuate flatulence. Providing soybean flour at <30 g/day may be prudent for overall health and to prevent the exclusion of other food groups and nutrients in older adults with obesity.

Exercise in the Prevention and Treatment of Type 2 Diabetes.

Type 2 diabetes is a systemic, multifactorial disease that is a leading cause of morbidity and mortality globally. Despite a rise in the number of available medications and treatments available for management, exercise remains a first-line prevention and intervention strategy due to established safety, efficacy, and tolerability in the general population. Herein we review the predisposing risk factors for, prevention, pathophysiology, and treatment of type 2 diabetes. We emphasize key cellular and molecular adaptive processes that provide insight into our evolving understanding of how, when, and what types of exercise may improve glycemic control. © 2023 American Physiological Society. Compr Physiol 13:1-27, 2023.

Effect of exercise training on insulin-stimulated glucose disposal: a systematic review and meta-analysis of randomized controlled trials.

BACKGROUND AND OBJECTIVE: The effect of exercise training on whole-body insulin sensitivity has not been systematically summarized. We aimed to summarize the data from randomized controlled trials evaluating the effect of exercise training on insulin action, in adults. SUBJECTS: MEDLINE, EMBASE, and CENTRAL databases were searched until January 2021. Randomized controlled trials lasting ≥4 weeks, including adults, and evaluating the effect of exercise on insulin-stimulated glucose disposal measured using the hyperinsulinemic euglycemic clamp, were included. METHODS: Three reviewers extracted summary data from published trials. The primary outcome was insulin-stimulated glucose disposal. Standardized weighted mean differences (SMD) in glucose disposal between intervention and control were compared. The PEDro scale was used to assess risk of bias. RESULTS: We included 25 trials (36 interventions, N = 851). Exercise increased insulin-stimulated glucose disposal relative to control, SMD = 0.52 (95% confidence interval [CI]: 0.39, 0.65; p < 0.001; I2 = 47%) without significantly suppressing hepatic glucose production. In trials without isotopic tracers, exercise increased glucose disposal (SMD = 0.63; 95% CI: 0.48, 0.77; p < 0.001, I2 = 55%). In trials with isotopic tracers, exercise increased glucose disposal only when tracers were added to the exogenous glucose used for clamping (SMD = 0.34; 95% CI: 0.03, 0.66, p = 0.034. I2 = 0%). In a meta-regression model including aerobic exercise, weight change, and tracer technique, only percent weight change explained between trial heterogeneity (ß = 0.069; 95% CI: 0.005, 0.013). The PEDro rating indicated relatively low risk of bias (5.8 ± 0.22). CONCLUSIONS: Exercise training for at least four weeks significantly increases insulin-stimulated glucose disposal. Weight loss maximizes the effect and may be needed to improve hepatic insulin sensitivity. Differences in tracer methodology contribute to divergent outcomes and should be considered when assessing conclusions from research examining the effect of exercise on insulin action. REGISTRATION: PROSPERO (CRD42019124381).

Association of Type 2 Diabetes Subgroups With Cognitive Status Without Modification From Lifestyle Intervention.

CONTEXT: Type 2 diabetes is a risk factor for incident dementia but whether risk and treatment/prevention strategies differ by diabetes subgroup is unknown. OBJECTIVE: We assessed (1) whether specific type 2 diabetes (T2D) subgroups are associated with mild cognitive impairment (MCI) or probable dementia (PD), and (2) whether T2D subgroups modified the association of the Action for Health in Diabetes (Look AHEAD) multidomain intensive lifestyle intervention (ILI) with MCI/PD. METHODS: We included 3760 Look AHEAD participants with T2D and overweight or obesity randomly assigned to 10 years of ILI or diabetes support and education. We used k-means clustering techniques with data on age of diabetes diagnosis, body mass index, waist circumference, and glycated hemoglobin (HbA1c) to characterize diabetes subgroups at randomization. Prevalent MCI/PD were centrally adjudicated based on standardized cognitive tests and other health information 10 to 13 years after randomization. We estimated marginal probabilities for prevalent MCI/PD among T2D subgroups with adjustment for potential confounders and attrition and examined whether ILI modified any associations. RESULTS: Four distinct T2D subgroups were identified, characterized by older age at diabetes onset (43% of sample), high HbA1c (13%), severe obesity (23%), and younger age at onset (22%). Unadjusted prevalence of MCI/PD (314 cases, 8.4%) differed across T2D subgroup (older onset = 10.5%, severe obesity = 9.0%, high HbA1c = 7.9%, and younger onset = 4.0%). Adjusted probability for MCI/PD within T2D subgroup was highest for the severe obesity subgroup and lowest for the younger onset subgroup but did not differ by ILI arm (interaction P value = 0.84). CONCLUSIONS: Among individuals with T2D and overweight or obesity, probability of MCI/PD differed by T2D subgroup. Probability of MCI/PD was highest for a subgroup characterized by severe obesity. CLINICALTRIALS.GOV IDENTIFIER: NCT00017953.

Low-Energy Dense Potato- and Bean-Based Diets Reduce Body Weight and Insulin Resistance: A Randomized, Feeding, Equivalence Trial.

We evaluated the effect of diets low in energy density (1 kcal/g) and high in either potatoes (Potato) or pulses (Bean) on blood glucose control in participants with insulin resistance. We hypothesized that the Potato and Bean diets would have equivalent effects. This was an 8-week randomized, parallel design, controlled feeding study comparing Potato and Bean diets (50-55% carbohydrate, 30-35% fat, 15-20% protein). Equivalence was prespecified as the mean change in the blood glucose concentration for Potato that was within ±20% of the Bean diet. Thirty-six participants (age: 18-60 years, body mass index: 25-40 kg/m2) with insulin resistance (homeostatic model assessment of insulin resistance [HOMA-IR] >2) were enrolled. Body weight was measured, and subjects underwent a mixed meal tolerance test at baseline and after 8 weeks. Intent-to-treat (ITT) and completer analyses were conducted. Equivalence between the two diets in the area under the curve for serum glucose was attained within ±10%, but the reduction from baseline was not statistically significant. For the Bean diet, insulin (area under the response curve: -2136.3 ± 955.5 mg/[dL∙min], P = .03) and HOMA-IR (-1.4 ± 0.6, P = .02) were lower compared with baseline. ITT and completer analyses were similar, except that HOMA-IR was also reduced by the Potato diet (-1.3 ± 0.6, P < .05). Compliance with the diets was 87-88%, and body weight was reduced in both diets (Potato: -5.6% ± 0.6%; Bean: -4.1% ± 0.6%, P < .001) with no significant difference between the two diets. Potato and Bean diets low in energy density were equally effective in reducing insulin resistance and promoting weight loss in individuals with impaired blood glucose control. Clinical Trial: The trial was registered with ClinicalTrials.gov Identifier: NCT04203238.

Sympathomimetic increases resting energy expenditure following bariatric surgery: A randomized controlled clinical trial.

OBJECTIVE: The aim of this study was to test the hypothesis that ephedrine + caffeine (EC) reduces the fall in resting energy expenditure (REE) following bariatric surgery. METHODS: This 32-week, randomized, double-blinded, placebo-controlled trial included 142 patients who underwent Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) surgery. Participants were randomized to either EC or placebo for 27 weeks, beginning 5 weeks post surgery. The primary end points were change in REE (measured), percentage of predicted REE ([measured REE/Harris-Benedict equation-predicted REE] × 100), and body composition. Secondary outcomes included change in percentage of weight. Adverse events (AEs) were recorded. RESULTS: The reduction in REE was smaller in the EC versus the placebo group, but it was not significant. Percentage of predicted REE was increased in the EC versus the placebo group (difference, mean [SE]: 5.82 [2.29], p = 0.013). Percentage of weight (difference: -3.83 [1.39], p = 0.007) was reduced in the EC versus the placebo group. Percentage of predicted REE was increased and body weight decreased in the EC-treated participants who underwent SG compared with those who underwent SG and were treated with placebo (difference in percentage of predicted REE = 8.06 [2.83], p = 0.006; difference in weight percentage = -4.37 [1.92], p = 0.025). Percentage of fat-free mass was increased in the SG participants treated with EC versus placebo (difference: 1.31 [0.63], p = 0.042). The most common AEs were anxiety, dizziness, insomnia, and tremors. Most AEs were not different from placebo by Week 32. CONCLUSIONS: EC enhances weight loss and reduces the fall in REE following bariatric surgery. Adrenergic symptoms mostly resolve over time.

Exercise as a Moderator of Persistent Neuroendocrine Symptoms of COVID-19.

Precipitated by chronic psychological stress, immune system dysregulation, and a hyperinflammatory state, the sequelae of postacute COVID-19 (long COVID) include depression and new-onset diabetes. We hypothesize that exercise counters the neuropsychiatric and endocrine sequelae of long COVID by inducing the release of circulating factors that mediate the anti-inflammatory response, support brain homeostasis, and increase insulin sensitivity.

MLR-1023 Treatment in Mice and Humans Induces a Thermogenic Program, and Menthol Potentiates the Effect.

A glucose-lowering medication that acts by a different mechanism than metformin, or other approved diabetes medications, can supplement monotherapies when patients fail to meet blood glucose goals. We examined the actions underlying the effects of an insulin sensitizer, tolimidone (MLR-1023) and investigated its effects on body weight. Diet-induced obesity (CD1/ICR) and type 2 diabetes (db/db) mouse models were used to study the effect of MLR-1023 on metabolic outcomes and to explore its synergy with menthol. We also examined the efficacy of MLR-1023 alone in a clinical trial (NCT02317796), as well as in combination with menthol in human adipocytes. MLR-1023 produced weight loss in humans in four weeks, and in mice fed a high-fat diet it reduced weight gain and fat mass without affecting food intake. In human adipocytes from obese donors, the upregulation of Uncoupling Protein 1, Glucose (UCP)1, adiponectin, Glucose Transporter Type 4 (GLUT4), Adipose Triglyceride Lipase (ATGL), Carnitine palmitoyltransferase 1 beta (CPT1ß), and Transient Receptor Potential Melastin (TRPM8) mRNA expression suggested the induction of thermogenesis. The TRPM8 agonist, menthol, potentiated the effect of MLR-1023 on the upregulation of genes for energy expenditure and insulin sensitivity in human adipocytes, and reduced fasting blood glucose in mice. The amplification of the thermogenic program by MLR-1023 and menthol in the absence of adrenergic activation will likely be well-tolerated, and bears investigation in a clinical trial.

Targeting the T-type calcium channel Cav3.2 in GABAergic arcuate nucleus neurons to treat obesity.

OBJECTIVE: Cav3.2, a T-type low voltage-activated calcium channel widely expressed throughout the central nervous system, plays a vital role in neuronal excitability and various physiological functions. However, the effects of Cav3.2 on energy homeostasis remain unclear. Here, we examined the role of Cav3.2 expressed by hypothalamic GABAergic neurons in the regulation of food intake and body weight in mice and explored the underlying mechanisms. METHODS: Male congenital Cana1h (the gene coding for Cav3.2) global knockout (Cav3.2KO) mice and their wild type (WT) littermates were first used for metabolic phenotyping studies. By using the CRISPR-Cas9 technique, Cav3.2 was selectively deleted from GABAergic neurons in the arcuate nucleus of the hypothalamus (ARH) by specifically overexpressing Cas9 protein and Cav3.2-targeting sgRNAs in ARH Vgat (VgatARH) neurons. These male mutants (Cav3.2KO-VgatARH) were used to determine whether Cav3.2 expressed by VgatARH neurons is required for the proper regulation of energy balance. Subsequently, we used an electrophysiological patch-clamp recording in ex vivo brain slices to explore the impact of Cav3.2KO on the cellular excitability of VgatARH neurons. RESULTS: Male Cav3.2KO mice had significantly lower food intake than their WT littermate controls when fed with either a normal chow diet (NCD) or a high-fat diet (HFD). This hypophagia phenotype was associated with increased energy expenditure and decreased fat mass, lean mass, and total body weight. Selective deletion of Cav3.2 in VgatARH neurons resulted in similar feeding inhibition and lean phenotype without changing energy expenditure. These data provides an intrinsic mechanism to support the previous finding on ARH non-AgRP GABA neurons in regulating diet-induced obesity. Lastly, we found that naringenin extract, a predominant flavanone found in various fruits and herbs and known to act on Cav3.2, decreased the firing activity of VgatARH neurons and reduced food intake and body weight. These naringenin-induced inhibitions were fully blocked in Cav3.2KO-VgatARH mice. CONCLUSION: Our results identified Cav3.2 expressed by VgatARH neurons as an essential intrinsic modulator for food intake and energy homeostasis, which is a potential therapeutic target in the treatment of obesity.

Leucine and Sildenafil Combination Therapy Reduces Body Weight and Metformin Enhances the Effect at Low Dose: A Randomized Controlled Trial.

BACKGROUND: This study evaluated the potential of activating the fuel-sensing enzymes Adenine monophosphate (AMP)-activated protein kinase and the deacetylase sirtuin1, to promote weight loss. We tested the efficacy of a fixed dose combination of the amino acid leucine and 2 well-characterized agents with established safety profiles to modulate energy metabolism and facilitate weight loss. STUDY QUESTION: Will a combination of l-leucine with low-dose metformin and sildenafil produce a novel synergistic interaction that reduces body weight? STUDY DESIGN: We conducted a 24-week randomized controlled trial evaluating the effect on weight loss of leucine 1.1 g and sildenafil 1.0 mg or 4.0 mg, with and without metformin 500 mg (Leu/Sil 1.0, Leu/Sil 4.0, Leu/Met/Sil 1.0, and Leu/Met/Sil 4.0 twice/day). We enrolled 267 participants who were 18-65 years of age without diabetes and with the body mass index (BMI) of 30-45 kg/m2. MEASURES AND OUTCOMES: The primary endpoint was percentage weight change after 24 weeks. Adverse events were evaluated. The primary analysis was performed using the perprotocol population analysis of covariance estimation. Subgroup analyses of patients residing above certain threshold limits at baseline and in populations at increased risk of obesity were assessed post-hoc as exploratory end points. RESULTS: Placebo-adjusted mean bodyweight reductions in the Leu/Met/Sil 1.0, Leu/Met/Sil 4.0, and Leu/Sil 4.0 groups were -1.99%, -1.69%, and -1.67% (P = 0.015, 0.035, and 0.036, respectively). The most common adverse events were gastrointestinal-related and occurred in the metformin-treated groups consistent with metformin treatment. In African Americans, Leu/Met/Sil 1.0 produced 5.4% mean weight loss. In participants with BMI <40 kg/m2 treated with Leu/Met/Sil 1.0, the weight loss increased to 2.84%, particularly in participants with baseline insulin ≥12mU/L (3.5%). CONCLUSIONS: Leu/Met/Sil 1.0 and 4.0 and Leu/Sil 4.0 reduced body weight, but Leu/Met/Sil 1.0 was associated with robust weight loss in African Americans, and individuals with BMI 30-39.9 kg/m2, especially participants with hyperinsulinemia.

Obesity, the most common comorbidity in SARS-CoV-2: is leptin the link?

Overweight and obesity are major risk factors for diabetes, cardiovascular disease, and lung disease. These diseases are the most commonly reported health conditions that predispose individuals with SARS-CoV-2 infection to require hospitalization including intensive care unit admissions. The innate immune response is the host's first line of defense against a human coronavirus infection. However, most coronaviruses are armed with one strategy or another to overcome host antiviral defense, and the pathogenicity of the virus is related to its capacity to suppress host immunity. The multifaceted nature of obesity including its effects on immunity can fundamentally alter the pathogenesis of acute respiratory distress syndrome and pneumonia, which are the major causes of death due to SARS-CoV-2 infection. Elevated circulating leptin concentrations are a hallmark of obesity, which is associated with a leptin-resistant state. Leptin is secreted by adipocytes in proportion to body fat and regulates appetite and metabolism through signaling in the hypothalamus. However, leptin also signals through the Jak/STAT and Akt pathways, among others, to modulate T cell number and function. Thus, leptin connects metabolism with the immune response. Therefore, it seems appropriate that its dysregulation would have serious consequences during an infection. We propose that leptin may be the link between obesity and its high prevalence as a comorbidity of the SARS-CoV-2 infection. In this article, we present a synthesis of the mechanisms underpinning susceptibility to respiratory viral infections and the contribution of the immunomodulatory effects of obesity to the outcome.

A Snack Formulated with Ingredients to Slow Carbohydrate Digestion and Absorption Reduces the Glycemic Response in Humans: A Randomized Controlled Trial.

This study compared the effect of a snack with ingredients to slow carbohydrate digestion (Test-snack) on postprandial blood glucose and insulin concentrations and subjective appetite ratings. We hypothesized that Test-snack would lower glucose and insulin responses and reduce appetite compared with a Control-snack. Overweight or obese subjects (n = 17) completed a randomized crossover study. Glucose, insulin, and appetite ratings were measured before consuming each snack or white bread (Bread) and over a period of 4 h. Subjects received Test-snack, Control-snack, or Bread in random order at least a week apart. The a priori primary outcome was the glucose response, and the secondary outcomes were appetite ratings and insulin responses. Mixed effects statistical models were used to perform analysis of variance in terms of the area under curve (AUC) and at specific time points. The 2-h AUC for glucose was significantly lower with Test-snack compared to Control-snack and Bread (AUC and 95% confidence intervals: Test = 2186.43 [1783.36-2589.51]; Control = 3293.75 [2893.97-3693.54]; Bread = 2800.28 [2405.79-3194.77] mg/dL · min). Four-hour AUC for glucose, and insulin, followed a similar pattern except that Test-snack did not differ from Bread. The glucose concentrations peaked at 45 min under all three conditions, but Test-snack elicited a lower response than Control-snack and Bread (P < .01). Test increased fullness and satisfaction and reduced hunger and prospective intake compared to Bread (P < .02), but was not significantly different from Control-snack. Ingredients that slow carbohydrate digestion in a snack reduce the postprandial glucose and insulin responses compared to a product without these ingredients.

Safety and pharmacokinetics of naringenin: A randomized, controlled, single-ascending-dose clinical trial.

AIMS: To evaluate the safety and pharmacokinetics of naringenin in healthy adults consuming whole-orange (Citrus sinensis) extract. METHODS AND METHODS: In a single-ascending-dose randomized crossover trial, 18 adults ingested doses of 150 mg (NAR150), 300 mg (NAR300), 600 mg (NAR600) and 900 mg (NAR900) naringenin or placebo. Each dose or placebo was followed by a wash-out period of at least 1 week. Blood safety markers were evaluated pre-dose and 24 hours post-dose. Adverse events (AEs) were recorded. Serum naringenin concentrations were measured before and over 24 hours following ingestion of placebo, NAR150 and NAR600. Four- and 24-hour serum measurements were obtained after placebo, NAR300 and NAR900 ingestion. Data were analysed using a mixed-effects linear model. RESULTS: There were no relevant AEs or changes in blood safety markers following ingestion of any of the naringenin doses. The pharmacokinetic variables were: maximal concentration: 15.76 ± 7.88 µM (NAR150) and 48.45 ± 7.88 µM (NAR600); time to peak: 3.17 ± 0.74 hours (NAR150) and 2.41 ± 0.74 hours (NAR600); area under the 24-hour concentration-time curve: 67.61 ± 24.36 µM × h (NAR150) and 199.05 ± 24.36 µM × h (NAR600); and apparent oral clearance: 10.21 ± 2.34 L/h (NAR150) and 13.70 ± 2.34 L/h (NAR600). Naringenin half-life was 3.0 hours (NAR150) and 2.65 hours (NAR600). After NAR300 ingestion, serum concentrations were 10.67 ± 5.74 µM (4 hours) and 0.35 ± 0.30 µM (24 hours). After NAR900 ingestion, serum concentrations were 43.11 ± 5.26 µM (4 hours) and 0.24 ± 0.30 µM (24 hours). CONCLUSIONS: Ingestion of 150 to 900 mg doses of naringenin is safe in healthy adults, and serum concentrations are proportional to the dose administered. Since naringenin (8 µM) is effective in primary human adipocytes, ingestion of 300 mg naringenin twice/d will likely elicit a physiological effect.