If couch-potato lab mice had beach-body dreams and if they could speak, they might tell you they’re thrilled by advances in the science of exercise and calorie-restriction (CR) mimetics.
In recent studies conducted at research centers across the United States, mice have chowed down, fattened up, exercised only if they felt like it, and still managed to lose body fat, improve their blood lipids, increase muscle power, avoid blood sugar problems, and boost heart function.
How did these mice get so lucky? They were given mimetics, experimental drugs that “mimic” the effects of exercise and calorie reduction in the body without the need to break a sweat or eat less.
“The mice looked like they’d done endurance training,” said Thomas Burris, PhD, chair of the Department of Pharmacodynamics at the University of Florida, Gainesville, Florida, and coauthor of a September 2023 study of the exercise mimetic SLU-PP-332, published in The Journal of Pharmacology and Experimental Therapeutics.
Meanwhile, the CR mimetic mannoheptulose (MH) “was incredibly effective at stopping the negative effects of a high-fat diet in mice,” said Donald K. Ingram, PhD, an adjunct professor at Louisiana State University’s Pennington Biomedical Research Center, Baton Rouge, Louisiana, who began studying CR mimetics at the National Institute on Aging in the 1980s. In a 2022 study published in Nutrients, MH also increased insulin sensitivity.
These “have your cake and eat it, too” drugs aren’t on the market for human use — but they’re edging closer. Several have moved into human trials with encouraging results. The National Institutes of Health and the pharmaceutical industry are taking notice, anteing up big research dollars. At the earliest, one could win US Food and Drug Administration (FDA) approval in 4-5 years, Dr. Burris said.
The medical appeal is clear: Mimetics could one day prevent and treat serious conditions such as age- and disease-related muscle loss, diabetes, heart failure, and even neurodegenerative disorders like Parkinson’s disease and Alzheimer’s disease, said the scientists studying them.
The commercial appeal is unavoidable: Mimetics have the potential to help nondieters avoid weight gain and allow dieters to build and/or preserve more calorie-burning muscle — a boon because losing weight can reduce muscle, especially with rapid loss.
How do these drugs work? What’s their downside? Like the “miracle” glucagon-like peptide 1 (GLP-1) weight-loss drugs that are now ubiquitous, are mimetics an effective pharmaceutical way to replicate two of society’s biggest lifestyle sticking points — diet and exercise?
It’s possible…
CR Mimetics: The Healthspan Drug?
From nematodes and fruit flies to yeast, Labrador Retrievers, and people, plenty of research shows that reducing calorie intake may improve health and prolong life. By how much? Cutting calories by 25% for 2 years slowed the pace of aging 2%-3% in the landmark CALERIE study of 197 adults, according to a 2023 study in Nature Aging. Sounds small, but the researchers said that equals a 10%-15% lower risk for an early death — on par with the longevity bonus you’d get from quitting smoking.
Trouble is low-cal living isn’t easy. “Diets work,” said George Roth, PhD, of GeroScience, Inc., in Pylesville, MD, who began studying CR at the National Institute on Aging in the 1980s with Ingram. “But it’s hard to sustain.”
That’s where CR mimetics come in. They activate the same health-promoting genes switched on by dieting, fasting, and extended periods of hunger, Dr. Roth said. The end result isn’t big weight loss. Instead, CR mimetics may keep us healthier and younger as we age. “Calorie restriction shifts metabolic processes in the body to protect against damage and stress,” he said.
Dr. Roth and Dr. Ingram are currently focused on the CR mimetic mannoheptulose (MH), a sugar found in unripe avocados. “It works at the first step in carbohydrate metabolism in cells throughout the body, so less energy goes through that pathway,” he said. “Glucose metabolism is reduced by 10%-15%. It’s the closest thing to actually eating less food.”
Their 2022 study found that while mice on an all-you-can-eat high-fat diet gained weight and body fat and saw blood lipids increase while insulin sensitivity decreased, mice that also got MH avoided these problems. A 2023 human study in Nutrients coauthored by Dr. Roth and Dr. Ingram found that a group consuming freeze-dried avocado had lower insulin levels than a placebo group.
Other researchers are looking at ways to stimulate the CR target nicotinamide adenine dinucleotide (NAD+). NAD+ assists sirtuins — a group of seven enzymes central to the beneficial effects of CR on aging — but levels drop with age. University of Colorado researchers are studying the effects of nicotinamide riboside (NR), an NAD+ precursor, in older adults with a $2.5 million National Institute on Aging grant. Small, preliminary human studies have found the compound reduced indicators of insulin resistance in the brain, in a January 2023 study in Aging Cell, and reduced blood pressure and arterial stiffness in a 2018 study published in Nature Communications.
Another NAD+ precursor, nicotinamide mononucleotide, reduced low-density lipoprotein cholesterol, diastolic blood pressure, and body weight in a Harvard Medical School study of 30 midlife and older adults with overweight and obesity, published in August 2023 in The Journal of Clinical Endocrinology & Metabolism. And in an April 2022 study published in Hepatology of people with nonalcoholic fatty liver disease, a proprietary supplement that included NR didn’t reduce liver fat but had a significant (vs placebo) reduction in ceramide and the liver enzyme alanine aminotransferase, a marker of inflammation.
“I think it was a pretty interesting result,” said lead researcher Leonard Guarente, PhD, professor of biology at Massachusetts Institute of Technology and founder of the supplement company Elysium. “Fatty liver progressively damages the liver. This has the potential to slow that down.”