family heirloom

Intermittent fasting could have unintended effects on future generations

Worms’ descendants suffered from their ancestors’ diets.

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When ordering that keto meal-prep service, embarking on a day-long fast, or blending up a smoothie to sustain you throughout the day, you are likely thinking about the potential health benefits. You are probably not thinking your potential unborn grandchildren — but maybe you should be.

It’s possible that playing around with our diet today could influence generations for years to come. Emerging findings suggest that it may be best to tread lightly with drastic diet regimens — especially when it comes to prolonged fasting or extreme calorie restriction.

Here’s the background — When our bodies undergo a change, it is tempting to think of ourselves as an island. But what happens in our lives can affect our offspring — and that is true of what happens to our bodies, too. On the most basic level, we know that prospective parents’ diets can affect their child’s health.

But it turns out it goes further than that. For example, some studies suggest that if a parent experiences famine, it is associated with a higher risk of stroke in their children.

A 2014 study involving 277 families in Sweden found similar: when grandparents had experienced a dramatic change in food availability (from more to less, or less to more), there was an increased risk of a heart attack in their grandchildren. Some grandchildren had changes in mental health, too.

Together, these studies provide compelling clues that we are what we eat — and so are our descendants. While famine is an extreme case, these findings also matter if you follow a strict diet regimen, or fast.

The food that was available to long-gone generations may have an effect on their descendants today.

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What the science shows — Much of what we know about dietary restriction and its effects on future generations comes from animal models.

Animal studies can hint at the questions for researchers to explore in humans to tease apart how our diets affect our offspring. To that end, most intergenerational studies use nematodes or roundworms as a proxy for humans.

“A lot about the biology and life history is obviously very different to humans,” Edward Ivimey-Cook tells Inverse.

“But [worms] do share similar molecular pathways which are activated when under stress, i.e. food limitation or fasting.” Ivimey-Cook is a senior research associate at the School of Biological Sciences at the University of East Anglia and an author on a new study that speaks to this idea of an intergenerational ripple effect from intermittent fasting.

In the study, published this month in Proceedings of the Royal Society B, nematodes were observed over three generations and across a number of dietary scenarios. The first generation, or great-great-grandparents, were split into groups that followed one of four conditions for two days, before returning to eating as they pleased and being allowed to reproduce. The regimens were as follows:

  • Temporary fast
  • Eating as much as they wanted
  • Temporary fast with exposure to the odor of food — a means to pique their appetite
  • Eating as much as they wanted with exposure to the odor of food

What they found — Interestingly, this first generation’s temporary fasting increased their lifespan. But their great-grandchildren had greater mortality and reduced “fitness” — which in this case, means reproductive abilities.

The humble nematode, or C elegans.


When a parental generation and their offspring experience the same dietary conditions — regardless of what they were — both experience the same benefits, but, crucially, only if the conditions stay the same. For example, parent worms who fasted increased their lifespan, and if their offspring also fasted, they too increased their lifespan and reproductive abilities. But survival and reproduction suffered if the offspring switched diets to have unlimited access to food. An abrupt change over a generation hurts offspring, it seems.

Interestingly, food odor seemed to spur reproduction, fasting or not. This suggests that the worms may be more likely to reproduce if they sense there are more resources available for their children.

Why it matters — As far as what this means for us humans, it’s very preliminary. But for followers of intermittent fasting and other diet regimens, it is worthwhile considering these studies. Of course, if you choose to change your diet, the best person to talk to is your healthcare provider.

“We can’t really make any direct comparisons with humans in relation to the findings from this study — only prompt consideration for further long-term research to look specifically as the effects of fasting in other organisms, including humans,” Ivimey-Cook says.

The findings from this study are consistent with past animal studies, which indicate fasting increases lifespan in some creatures — a good sign for proponents of intermittent fasting and its claims to boosting longevity.

Yet they also reinforce that dietary restriction has costs. Previous research shows how fruit flies that returned to a standard diet after fasting reduced their own survival and reproduction. When it came to future offspring, another study suggests that a dietary switch over a generation harmed the offspring of fasting parent worms.

We aren’t worms — but we can learn from these multigenerational experiments: big changes in diet may yield unexpected changes after we’re long gone.

Abstract: Dietary restriction (DR) increases lifespan in a broad variety of organisms and improves health in humans. However, long-term transgenerational consequences of dietary interventions are poorly understood. Here, we investigated the effect of DR by temporary fasting (TF) on mortality risk, age-specific reproduction and fitness across three generations of descendants in Caenorhabditis elegans. We show that while TF robustly reduces mortality risk and improves late-life reproduction of the individuals subject to TF (P0), it has a wide range of both positive and negative effects on their descendants (F1–F3). Remarkably, great-grandparental exposure to TF in early life reduces fitness and increases mortality risk of F3 descendants to such an extent that TF no longer promotes a lifespan extension. These findings reveal that transgenerational trade-offs accompany the instant benefits of DR, underscoring the need to consider fitness of future generations in pursuit of healthy ageing.
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