While many of us are looking forward to a Thanksgiving meal with all the trimmings, new studies show that fasting, not feasting, may be better for our health. The potential health benefits of fasting have long intrigued scientists, and new animal studies have shed light on how fasting impacts the body in ways that may also benefit humans.
Fewer Calories, Longer Life
A new study from The Jackson Laboratory and Calico Life Sciences has that found eating fewer calories may extend the life span of mouse models.
Researchers assigned five different diets to 960 genetically diverse female mice: daily calories restricted 40% or 20% from baseline, fasting for one or two consecutive days each week with no caloric restrictions, or unlimited calorie consumption. The longest-lived mice were those on the 40% restricted calorie diet, living an average of five months longer than the shortest-lived mice—those on the unlimited-calorie diet.
However, while the team found that consuming fewer calories could extend life span, the mice that lived the longest didn’t necessarily lose the most weight. Surprisingly, genetics, particularly genetically encoded resilience, seemed to play a larger role in longevity than diet, with some mice retaining body weight yet living longer. This finding challenges previous claims that weight loss alone leads to a longer life.
Although promising, translating these animal findings to humans requires further study to understand how fasting and diet can best promote health and longevity in people.
Pluses and Minuses of Fasting
Like everything, it seems fasting has an upside and a downside. Previous research at MIT found that fasting can enhance the regenerative capacity of intestinal stem cells, helping the intestine heal from injuries or inflammation.
A new study zeroed in on the precise mechanism responsible for this improved regeneration: the mTOR pathway, which activates when mice begin eating again after a fast, causing more protein to be produced.
When mTOR is activated, it produces elevated levels of polyamines, which drive cell growth and division. However, this enhanced regeneration and cell growth has a drawback: if exposed to cancerous mutations during this regenerative phase, the mice showed a higher likelihood of developing early-stage intestinal tumors.
It’s unclear whether the same effect occurs in humans.
Fasting to Fight Cancer
According to a new study fromMemorial Sloan Kettering Cancer Center, fasting can do more than help you lose weight, it may help your body fight cancer.
The study suggests that fasting twice a week for 24 hours enhances the cancer-fighting ability of immune cells known as natural killer (NK) cells—white blood cells that not only attack virus-infected and cancerous cells but also release signaling proteins, cytokines, to mobilize other immune cells against harmful cells.
In the study, researchers fasted cancer-affected mice twice weekly for 24 hours, allowing free eating between fasts. This fasting cycle lowered the mice’s glucose levels and increased free fatty acids, which NK cells used as an alternative energy source, optimizing their response to tumors. This metabolic adaptation enabled NK cells to better survive within the tumor’s lipid-rich environment.
Fasting also caused NK cells to migrate to the bone marrow, where they encountered high levels of Interleukin 12, a protein that increased their production of anti-tumor cytokines like Interferon-gamma. Together, these adaptations boosted the NK cells’ ability to combat cancer.
The researchers are now studying if NK cells receive distinct training in the spleen or bone marrow, or if they move through both areas. This research supports fasting as a potential supplemental therapy to chemotherapy and may inspire treatments that mimic fasting’s effects without the need to fast.
Fasting to Reset Circadian Rhythms & Protect Against Alzheimer’s
Researchers at the University of California, San Diego have found that time-restricted feeding (TRF) may help lower the risk of cognitive decline and could benefit those with Alzheimer’s disease (AD).
In a recent study, they observed that restricting feeding in a mouse model of Alzheimer’s to a six-hour daily window, the equivalent of a 14-hour fast in humans, helped reset circadian rhythms, improving memory and reducing the buildup of amyloid, a protein linked to AD progression.
The team found that TRF helped regulate blood glucose levels, reduce neuroinflammation, and modify gene expression, which seemed to slow the disease. Female mice particularly showed increased sleep duration, while both sexes had improved sleep onset and less hyperactivity.
After three months, mice following TRF showed significant reductions in amyloid plaques and nearly matched the cognitive performance of healthy mice in tests.
While researchers are exploring TRF’s effects in humans, they encourage consulting with healthcare providers before starting fasting routines, as fasting impacts vary.
Intermittent Fasting to Improve Intestinal Functioning
Researchers at Midwestern University have discovered that intermittent fasting can help the body process glucose more effectively, improving age-related declines in intestinal function.
Using 32 mice genetically modified to accelerate aging, the team gave some mice unlimited access to food while others were fed every other day. After eight months, the mice on the every-other-day feeding schedule had gained less weight than the unlimited feeding group. In addition, the jejunum portion of the small intestines of the intermittent fasting mice exhibited structural changes associated with improved glucose control and reduced inflammation.
The effects were more pronounced in the female mice, which showed greater differences in overall health and the condition of the small intestine. However, the glucose effect was stronger in the male mice.
Numerous studies have linked Intermittent fasting with weight loss, but this study suggests that the weight-loss effect may be due at least in part to glucose metabolism in addition to calorie restriction.
