Smell of fatty food during pregnancy may prime children for obesity

The smell of bacon in pregnant mice’s low-fat diet was enough to make their pups gain extra weight later on. The study from Cologne, Germany, suggests that the smell of fatty food during pregnancy can quietly prime lifelong obesity risk.

Scientists already know that children of mothers with obesity face higher odds of obesity and chronic illness as adults. 

This new research on mice asks whether even a lean mother’s fatty-flavored diet during pregnancy can steer her offspring toward obesity later on.

Smell reaching the womb

The smell of fatty food can enter amniotic fluid, the liquid that surrounds a fetus in the womb. Classic feeding experiments have found that babies accept those familiar flavors more readily months later.

The work was led by Sophie M. Steculorum, a neuroscientist at the Max Planck Institute for Metabolism Research (MPI) in Cologne, Germany. 

Her research focuses on how early sensory experiences program the neural circuits that regulate appetite and whole-body metabolism.

Sensory signals in food

Smell is a major driver of what and how much people eat, often guiding food choices even more strongly than taste or appearance. 

By focusing on smell during pregnancy, the team could separate the calories in the mother’s diet from the sensory signals reaching the fetus.

In the new study, pregnant mice ate standard, low-fat chow that had been flavored to smell like bacon. 

The flavored diet had the same calories and nutrients as ordinary chow, and the mothers stayed lean with normal blood sugar, hormones, and body fat.

Insulin and dopamine response

When the offspring reached adulthood and ate a high-fat diet, they gained more weight than control mice from unscented pregnancies. 

They also carried more body fat and showed insulin resistance. This happens when cells stop responding properly to insulin, a warning sign for type 2 diabetes.

Brain scans and recordings in the offspring revealed altered responses in dopamine, a brain chemical that helps signal reward and motivation. 

The reward circuits reacted more strongly to high-fat cues and less to regular chow, similar to patterns already present in obese mice.

Activating hunger neurons

Another set of cells, AgRP neurons, became oddly insensitive to dietary fat. These hunger neurons sit in the brain’s hypothalamic region that drives eating.

The combined neural changes left the offspring’s lean brains signaling much like brains shaped by long-term obesity.

The young adult mice did not eat more overall than controls when given only the high-fat diet. Extra pounds came mainly from the way their bodies handled and burned calories, not from bigger meals.

Early brain programming

Researchers sometimes talk about metabolic programming, early life cues that lock in how organs handle food and stress. 

Fat-like smells paired with ordinary calories acted as a training signal that prepared the body for very rich food later.

The researchers saw weaker responses in brown fat, a heat-producing fat that burns energy, when the animals smelled and ate fatty food. 

Instead of ramping up heat output to burn extra calories, their bodies conserved energy, which helps explain the extra weight gain.

Impacts on female mice

Importantly, animals that only smelled the fatty diet without eating it did not show the same extra weight gain. 

Neonatal mice, whose odor circuits were activated with light, also stayed metabolically normal when the smell stimulation was not paired with calorie-rich feeding.

Early exposure to the odor acetophenone – a flavoring chemical – also caused weight gain specifically in female mice on a high-fat diet with the same smell.

Acetophenone appears in the FDA’s Substances Added to Food inventory as a flavoring agent or adjuvant.

That does not automatically make it harmful, but it shows that everyday foods already contain compounds capable of programming metabolism in mice.

What this could mean for people

In humans, children born to mothers with obesity face higher risks of obesity and other chronic illnesses, as summarized in a recent review. 

This new research on mice add to that picture by highlighting sensory qualities of food, rather than calories alone, as possible contributors to risk.

“That flavor transfer from mother to baby means modern processed foods can send complex odor and additive signals into the womb and into milk,” explained Steculorum.

The research results come from mice, so they cannot predict exact effects in people or replace medical advice for pregnant women. 

However, these findings highlight how early the sensory environment can shape biology and why future studies may need to track food smells during pregnancy.

The study is published in the journal Nature Metabolism.

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