Dietary Mannoheptulose Does Not Significantly Alter Daily Energy Expenditure in Adult Labrador Retrievers

Effects of an Unripe Avocado Extract on Glycaemic Control in Individuals with Obesity: A Double-Blinded, Parallel, Randomised Clinical Trial

BACKGROUND

Unripe avocados (Persea americana) are naturally enriched in mannoheptulose (MH), which is a candidate caloric restriction mimetic.

OBJECTIVES

To evaluate the effects of a diet supplement made from unripe avocado on glucose tolerance, and cardiometabolic risk factors in free-living nondiabetic adults with obesity.

METHODS

In a double-blinded, randomised controlled trial, 60 adults (female n = 47, age 48 ± 13 years, BMI 34.0 ± 2.6 kg/m2) were stratified by sex and randomised to avocado extract (AvX, 10 g finely ground, freeze-dried unripe avocado) or placebo (10 g finely ground cornmeal plus 5% spinach powder) daily, for 12 weeks. The primary outcome was a change in glucose area under the curve (AUC) in response to a 75 g oral glucose tolerance test. A post-hoc analysis was subsequently performed in a subgroup with insulin AUC above the median of baseline values after removal of participants >2 SD from the mean.

RESULTS

There were no between-group differences in glucose AUC (p = 0.678), insulin AUC (p = 0.091), or cardiovascular outcomes. In the subgroup analysis, insulin AUC was lower in AxV versus placebo (p = 0.024).

CONCLUSIONS

Daily consumption of unripe avocado extract enriched in MH did not alter glucose tolerance or insulin sensitivity in nondiabetic adults with obesity, but the data provided preliminary evidence for a benefit in insulin AUC in a subgroup of participants with elevated baseline postprandial insulin levels.

An Avocado Extract Enriched in Mannoheptulose Prevents the Negative Effects of a High-Fat Diet in Mice

Beginning at 16 weeks of age and continuing for 44 weeks, male C57BL/6J were fed either a control (CON) diet; a high-fat (HF) diet (60% unsaturated); or the HF diet containing an extract of unripe avocados (AvX) enriched in the 7-carbon sugar mannoheptulose (MH), designed to act as a glycolytic inhibitor (HF + MH). Compared to the CON diet, mice on the HF diet exhibited higher body weights; body fat; blood lipids; and leptin with reduced adiponectin levels, insulin sensitivity, VO2max, and falls from a rotarod. Mice on the HF + MH diet were completely protected against these changes in the absence of significant diet effects on food intake. Compared to the CON diet, oxidative stress was also increased by the HF diet indicated by higher levels of total reactive oxygen species, superoxide, and peroxynitrite measured in liver samples by electron paramagnetic resonance spectroscopy, whereas the HF + MH diet attenuated these changes. Compared to the CON, the HF diet increased signaling in the mechanistic target of the rapamycin (mTOR) pathway, and the addition of the MH-enriched AvX to this diet attenuated these changes. Beyond generating further interest in the health benefits of avocados, these results draw further new attention to the effects of this rare sugar, MH, as a botanical intervention for preventing obesity.

Roles of plant-based ingredients and phytonutrients in canine nutrition and health

Dogs possess the ability to obtain essential nutrients, established by the Association of American Feed Control Officials (AAFCO), from both animal‐ and plant‐based ingredients. There has been a recent increase in the popularity of diets that limit or completely exclude certain plant‐based ingredients. Examples of these diets include ‘ancestral’ or ‘evolutionary’ diets, raw meat‐based diets and grain‐free diets. As compared to animal sources, plant‐derived ingredients (including vegetables, fruits, grains, legumes, nuts and seeds) provide many non‐essential phytonutrients with some data suggesting they confer health benefits. This review aims to assess the strength of current evidence on the relationship between the consumption of plant‐based foods and phytonutrients (such as plant‐derived carotenoids, polyphenols and phytosterols) and biomarkers of health and diseases (such as body weight/condition, gastrointestinal health, immune health, cardiovascular health, visual function and cognitive function) from clinical trials and epidemiological studies. This review highlights the potential nutritional and health benefits of including plant‐based ingredients as a part of balanced canine diets. We also highlight current research gaps in existing studies and provide future research directions to inform the impact of incorporating plant‐based ingredients in commercial or home‐prepared diets.

Caloric Restriction Mimetics in Nutrition and Clinical Trials

The human diet and dietary patterns are closely linked to the health status. High-calorie Western-style diets have increasingly come under scrutiny as their caloric load and composition contribute to the development of non-communicable diseases, such as diabetes, cancer, obesity, and cardiovascular disorders. On the other hand, calorie-reduced and health-promoting diets have shown promising results in maintaining health and reducing disease burden throughout aging. More recently, pharmacological Caloric Restriction Mimetics (CRMs) have gained interest of the public and scientific community as promising candidates that mimic some of the myriad of effects induced by caloric restriction. Importantly, many of the CRM candidates activate autophagy, prolong life- and healthspan in model organisms and ameliorate diverse disease symptoms without the need to cut calories. Among others, glycolytic inhibitors (e.g., D-allulose, D-glucosamine), hydroxycitric acid, NAD+ precursors, polyamines (e.g., spermidine), polyphenols (e.g., resveratrol, dimethoxychalcones, curcumin, EGCG, quercetin) and salicylic acid qualify as CRM candidates, which are naturally available via foods and beverages. However, it is yet unclear how these bioactive substances contribute to the benefits of healthy diets. In this review, we thus discuss dietary sources, availability and intake levels of dietary CRMs. Finally, since translational research on CRMs has entered the clinical stage, we provide a summary of their effects in clinical trials.

Characterization and Mechanisms of Action of Avocado Extract Enriched in Mannoheptulose as a Candidate Calorie Restriction Mimetic

Increased consumer interest in the avocado (Persea americana or Persea gratissima) has been attributed to established health benefits of this fruit associated with a wide range of ingredients. In search of effective calorie restriction mimetics (CRM), we present herein a consideration of possible health benefits of the rare sugar, mannoheptulose (MH), which acts as an intracellular glycolytic inhibitor and presents the highest concentration of this inhibitor in unripe avocados. A method for producing an extract of unripe avocado (AvX) to enrich concentrations of MH is described. Experiments using myocyte cultures demonstrated a pattern of CRM-like responses when treated with AvX. In vivo experiments confirmed that orally consumed AvX is bioavailable in both mice and dogs, as observed in urine and blood samples. Additional experiments in both these species demonstrated CRM-like improvements in glucose and insulin responses. In sum, the MH-enriched AvX exhibits promise as a CRM.

Glycolytic inhibition: an effective strategy for developing calorie restriction mimetics

Calorie restriction mimetics encompass a growing research field directed toward developing treatments that mimic the anti-aging effects of long-term calorie restriction without requiring a change in eating habits. A wide range of approaches have been identified that include (1) intestinal inhibitors of fat and carbohydrate metabolism; (2) inhibitors of intracellular glycolysis; (3) stimulators of the AMPK pathway; (4) sirtuin activators; (5) inhibitors of the mTOR pathway, and (6) polyamines. Several biotech companies have been formed to pursue several of these strategies. The objective of this review is to describe the approaches directed toward glycolytic inhibition. This upstream strategy is considered an effective means to invoke a wide range of anti-aging mechanisms induced by CR. Anti-cancer and anti-obesity effects are important considerations in early development efforts. Although many dozens of candidates could be discussed, the compounds selected to be reviewed are the following: 2-deoxyglucose, 3-bromopyruvate, chrysin, genistein, astragalin, resveratrol, glucosamine, mannoheptulose, and D-allulose. Some candidates have been investigated extensively with both positive and negative results, while others are only beginning to be studied.

Reducing Glucokinase Activity to Enhance Insulin Secretion: A Counterintuitive Theory to Preserve Cellular Function and Glucose Homeostasis

Pancreatic beta-cells are the only cells in the body that can synthesize and secrete insulin. Through the process of glucose-stimulated insulin secretion, beta-cells release insulin into circulation, stimulating GLUT4-dependent glucose uptake into peripheral tissue. Insulin is normally secreted in pulses that promote signaling at the liver. Long before type 2 diabetes is diagnosed, beta-cells become oversensitive to glucose, causing impaired pulsatility and overstimulation in fasting levels of glucose. The resulting hypersecretion of insulin can cause poor insulin signaling and clearance at the liver, leading to hyperinsulinemia and insulin resistance. Continued overactivity can eventually lead to beta-cell exhaustion and failure at which point type 2 diabetes begins. To prevent or reverse the negative effects of overstimulation, beta-cell activity can be reduced. Clinical studies have revealed the potential of beta-cell rest to reverse new cases of diabetes, but treatments lack durable benefits. In this perspective, we propose an intervention that reduces overactive glucokinase activity in the beta-cell. Glucokinase is known as the glucose sensor of the beta-cell due to its high control over insulin secretion. Therefore, glycolytic overactivity may be responsible for hyperinsulinemia early in the disease and can be reduced to restore normal stimulus-secretion coupling. We have previously reported that reducing glucokinase activity in prediabetic mouse islets can restore pulsatility and enhance insulin secretion. Building on this counterintuitive finding, we review the importance of pulsatile insulin secretion and highlight how normalizing glucose sensing in the beta cell during prediabetic hyperinsulinemia may restore pulsatility and improve glucose homeostasis.

Dietary mannoheptulose does not alter glucose or lipid metabolism in adult Labrador Retrievers

Mannoheptulose (MH), a glycolytic inhibitor, has been preliminarily investigated as a novel functional food ingredient for dogs. This study aimed to determine the effects of dietary MH, delivered as an extract of un-ripened avocados, on fatty acid and glucose kinetics in healthy adult Labrador Retriever dogs (n = 12 dogs). The study was a double-blindcrossover with each dog receiving both dietary treatments, control (CON) and MH (400 mg/kg of diet), in random order. Glucose and glycerol plasma turnover (Ra) and oxidation (Ox) were measured in fasting and in response to repeated meal feeding ("fed") with stable isotope tracers (U-¹³ C-glucose, 1,1,2,3,3-D₅ -glycerol) and indirect calorimetry. Palmitate Ra and Ox were examined during repeated meal feeding only using an oral bolus of U-¹³ C-K₂ -palmitate and indirect calorimetry. MH had no discernible effect on fasting glucose Ra (677, 722 SEM 36 μmol/min, CON, MH) or Ox (107, 109 μmol/min, CON, MH SEM 10 μmol/min) or fed glucose Ra (2913, 3626 SEM 644 μmol/min, CON, MH) or Ox (951, 936 SEM 174 μmol/min, CON, MH). Glycerol Ra, an index of the rate of lipolysis, was not different between dietary treatments (Fast 162, 113 SEM 35 μmol/min CON, MH; Fed 172, 135 SEM 21 μmol/min, CON, MH). Similarly, palmitate oxidation was not impacted by MH feeding (1966, 2276 SEM 79 μmol/min, CON, MH). Together, these findings do not support MH as a novel functional food ingredient at least at the dietary dose tested.