Valter Longo

What Valter says, topic by topic

Protein

A 2014 paper from Longo’s lab, with him as senior author, used a large US national nutrition survey. Among people aged 50 to 65, those who reported the most protein had about 75% higher death rates over the next 18 years, and roughly four times the risk of dying of cancer¹. The authors reported that these links vanished or weakened when the protein came from plants¹.

After age 65 the pattern turned around in that study: more protein went with fewer cancer and overall deaths, although high protein was tied to a five-fold higher risk of dying of diabetes at all ages¹. Mouse tests in the same paper agreed, and also showed harm from a low protein diet in very old mice. The authors concluded that eating little protein in midlife and moderate to high amounts in old age may give the longest healthy life; this is an association study plus animal work, and his later advice may have moved on¹.

What all the experts say about protein

Fasting

The documentary Science of Fasting (posted 2021) shows an early test from Longo’s lab: mice with cancer fasted for 48 hours before very high doses of chemotherapy. Longo recalled that his graduate students first found the idea absurd, since starving something is expected to weaken it². He said a colleague phoned to report that all the fasted mice were alive and all the normally fed ones were dead, and that repeat runs gave the same result; these were results in mice, not people³.

His explanation, in the same film, is that low glucose and nutrients push normal cells into a protective standby mode learned over billions of years of evolution⁴. Cancer cells, carrying mutations, fail to make that switch: he said they become more sensitive to chemotherapy, and that fasting alone can slow their growth or kill some of them⁵.

Longo’s group also makes a commercial fasting product. Fasting clinician Alan Goldhamer said in 2025 that ProLon, a five-day kit eaten in place of normal food, comes from Longo’s group and costs about 250 dollars⁶.

What all the experts say about fasting

Cancer

In the documentary Science of Fasting (posted 2021), Longo told how mice that fasted before extreme doses of chemotherapy survived while normally fed mice died⁷. His explanation was that healthy cells shield themselves when food is scarce, while cancer cells, because of their mutations, cannot do so and end up more exposed to the drugs⁵.

His 2015 paper reported that in mice, repeated cycles of a fasting-mimicking diet begun in middle age lowered the number of tumors and pushed back tumor deaths by more than three months⁸. His 2014 protein study linked high protein at ages 50 to 65 with about four times the risk of cancer death, and in mice high protein sped up breast and melanoma tumors; both are animal or survey findings, not trials in patients¹.

What all the experts say about cancer

Dementia and the brain

In his 2015 paper on the fasting-mimicking diet, old mice that went through repeated diet cycles made more new nerve cells in the hippocampus, a brain area used for memory, and scored better than control mice on learning and memory tests⁸. These were results in mice only⁸.

What all the experts say about dementia and the brain

Longevity and aging

Longo’s work on aging centers on growth signals. His 2014 paper started from the fact that mice and people lacking the growth hormone receptor, and so low in the hormone IGF-1, have far fewer age-related diseases; since cutting protein lowers that signal, the team looked at protein and death rates (see Protein)¹.

His 2015 paper in Cell Metabolism described a five-day, plant-based, low-protein and low-calorie meal plan meant to bring the effects of fasting while still supplying food, called the fasting-mimicking diet⁸. In mice, cycles started in middle age raised median lifespan by about 11%, from 25.5 to 28.3 months, without changing maximum lifespan; the mice also had less belly fat, slower bone loss and a younger immune system⁸.

The same paper reported a pilot trial in 38 healthy adults, 19 of whom completed three diet cycles. The researchers found lower risk markers for aging, diabetes, heart disease and cancer, about 3% weight loss and no major side effects⁸. The paper discloses that Longo holds equity in L-Nutra, the company developing the diet, and that USC licensed the diet to it⁸.

What all the experts say about longevity and aging

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