Why What We Feed Babies Matters

What the science tells us about early sugar exposure, brain wiring, gut health, lifelong cravings — and the long reach of insulin resistance.

Why This Matters to Me

My fascination with food and the human body goes back a long way: As a young teenager, I started noticing the connection between what I ate and how I felt. It carried me into midwifery, where I have spent years working closely with mothers and babies — supporting women through pregnancy, birth, and those precious, demanding early months. More recently, I completed my training as a nutritional coach through Food Matters, which gave me a deeper framework for the importance of what we eat and what we feed our families.

What follows is one of the topics I feel most passionate about sharing. And it starts earlier than most people realise. There's a window of time, the first thousand days of a baby's life, from conception to age two, that researchers are increasingly calling one of the most important periods in human development. Not just for physical growth, but for something that will quietly influence the way that child eats, feels, and manages their health for the rest of their life.

What we are learning is this: feed a baby a diet high in sugar and processed foods during that window, and you may be doing more than filling a small stomach. You may be wiring their brain, disrupting their gut, and laying the groundwork for lifelong health consequences.

The First Year: A Brain Under Construction

By a baby's first birthday, their brain has doubled in size and reached about 70% of its adult size. The speed of development happening inside that little head is extraordinary, and it will never happen at this pace again.

During this time, the brain is building millions of connections between nerve cells, laying down the wiring that will shape how your child thinks, feels, learns, and what foods they crave. Think of it like electrical wiring being installed in a new house. Once it's in, it takes serious work to change it.

When a baby is repeatedly given sweet, ultra-processed foods, e.g. sugary fruit pouches, flavoured cereals, biscuits, juice, their developing brain takes note. The brain learns from repetition. What it experiences regularly, it wires itself toward.

What the Research Shows

Taste preferences can get set for life

Neuroscientist Dr. Amy Reichelt from the University of Adelaide has spent years researching how early diet shapes the developing brain. Her findings are striking: the young brain's remarkable capacity for learning also makes it unusually vulnerable to being shaped by diet. Because taste and reward associations form during critical developmental windows, they can become hardwired, making healthy eating genuinely harder to choose later in life. This is not about willpower. It is about how the brain was built.

Real children, real brain scans

One of the most compelling pieces of evidence comes from the Generation R study — a large Dutch project which followed nearly 2,000 children from infancy to age ten, then examined their brains using MRI scans. Children who had eaten a diet high in snacks, processed foods, and sugar at age one had measurably smaller brain volume at age ten, including smaller white matter, which is essentially the brain's internal communication network. These were real children eating the kind of diet that millions of babies in the developed world eat routinely.

It starts before birth

The vulnerable window actually begins before a baby takes their first bite. Research has found that a mother's sugar intake during pregnancy can affect how the baby's brain cells develop, specifically the branching structures that allow nerve cells to connect and communicate. More sugar in pregnancy can mean the baby arrives with less neural scaffolding to build on. The first year of feeding does not start on a blank slate.

Sugar and the brain's reward system

Sugar doesn't just taste nice — it activates the same reward pathway in the brain that is involved in addictive behaviours. Repeated sugar exposure causes real changes in this system, altering how the brain processes pleasure and satisfaction. When a baby's reward system is calibrated early to intensely sweet, processed foods, whole foods simply don't register as satisfying in the same way. The bar for what feels rewarding gets set artificially high.

The gut-brain connection

There is a third way that early sugar shapes long-term health. The gut microbiome, which begins forming at birth and reaches a relatively stable composition by around age three, plays a direct role in brain development and emotional regulation through what researchers call the microbiota-gut-brain axis.

Research published in Nutrients describes this window in time, a period when disruptions to gut flora can leave lasting imprints on the developing brain and nervous system. A high-sugar, low-fibre diet is one of the most potent disruptors of healthy gut bacteria in infancy, crowding out beneficial microbes and feeding those associated with inflammation.

The consequences show up later. A 2025 study published in Nature Communications followed children from age two to school age and found that the composition of gut microbes at age two predicted anxiety and internalising symptoms, e.g. withdrawal, worry, and low mood, in middle childhood, mediated by measurable changes in brain network connectivity. What was living in a two-year-old's gut was shaping how their brain processed emotion years later.

The effects extend further still. Research has linked high sugar intake in toddlers to sleep problems, ADHD symptoms, and anxiety. Sugar has the capacity to overstimulate a developing nervous system, contributing to mood swings and difficulty settling. This is perhaps the most profound extension of the early nutrition story: feeding a baby's gut well is, in a very real sense, feeding their future mental health.

The Long Shadow of Insulin Resistance

All of the above describes what happens in the brain and gut. But the downstream effects extend further still, into one of the most serious and underappreciated health conditions of our time: insulin resistance.

What is insulin resistance?

Insulin is the hormone your body uses to manage blood sugar. Think of it as a key that unlocks your cells so that glucose can enter and be used for energy. Insulin resistance happens when your cells stop responding properly to that key. The body compensates by producing more and more insulin to get the job done. Over time, this places enormous strain on the entire system, and according to clinical research, it can silently precede a Type 2 diabetes diagnosis by ten to fifteen years.

Why it matters far beyond blood sugar

Insulin resistance is not just a diabetes risk. Once it takes hold, its reach is extensive:

•High blood pressure and elevated triglycerides

•Non-alcoholic fatty liver disease

•Chronic low-grade inflammation throughout the body

•Damage to blood vessel walls, which is a key driver of heart disease and stroke

•Polycystic ovary syndrome (PCOS) in women

•Increased risk of certain cancers

•Links to Parkinson's disease and other neurodegenerative conditions

•The brain itself begins to struggle to use glucose efficiently, affecting memory, mood, and cognition

How the early years connect

A child whose brain has been wired toward ultra-processed, high-sugar foods will, without significant intervention, continue eating those foods. That dietary pattern, sustained across childhood and adolescence, is one of the primary drivers of insulin resistance. By the time that person reaches their thirties or forties, they may be experiencing unexplained fatigue, stubborn weight gain, brain fog, disrupted sleep, or a prediabetes result on a blood test. The seeds of that picture may have been planted in a highchair.

What This Means in Practice

None of this is meant to make parents feel guilty. They are usually doing their absolute best, often in the face of a food industry that has deliberately engineered and marketed ultra-processed products to babies and toddlers for decades. But knowledge is power, and the research gives us clear, practical principles:

•Delay added sugars and processed foods for as long as possible, ideally through the whole first year, and keep them minimal into toddlerhood.

•Introduce a wide variety of whole foods during weaning: vegetables (including bitter ones), legumes, wholegrains, healthy fats, and proteins. Variety helps calibrate the palate toward real food.

•Be cautious with fruit pouches and juices, they deliver concentrated sugar without the fibre and satiety of whole fruit.

•Remember that pregnancy nutrition counts too. What a mother eats shapes her baby's brain and gut before they're even born.

•For older children and adults already showing signs of insulin resistance, fatigue, sugar cravings, and energy crashes, reducing refined carbohydrates and moving toward whole food eating makes a measurable difference.

The Bottom Line

What we feed a baby is not just a nutrition question. It is a developmental one, shaping their brain, their gut, their cravings, their mental health, and their metabolic health for decades to come. The trajectory toward chronic disease can begin very early, but so can prevention.

As a midwife and lactation consultant, I sit with mothers at exactly this moment — right at the start of it all. And as a nutritional coach, I want to help them understand what that moment means. Not with fear, but with clarity and confidence.

Feed the brain well. Feed the gut well. From the very beginning.

Key Research & Further Reading

1.Generation R Study — Infant diet at age 1 and brain volume at age 10 — PMC10232626 — European Journal of Epidemiology, 2023

2.Prenatal sugar consumption and infant brain development — PMC8308814 — Nutrients, 2021

3.Dr. Amy Reichelt — Unpacking sugar's effects on kids' brains — University of Adelaide Research, 2024

4.Priming for Life: Early Life Nutrition and the Microbiota-Gut-Brain Axis — PMC7912058 — Nutrients, 2021

5.Childhood gut microbiome linked to internalising symptoms via brain connectivity — Nature Communications, 2025

6.Insulin Resistance — StatPearls Clinical Reference — NCBI Bookshelf, 2023

7.Advances in Insulin Resistance — Molecular Mechanisms and Therapeutic Targets — International Journal of Molecular Sciences, 2025

8.The crucial role and mechanism of insulin resistance in metabolic disease — Frontiers in Endocrinology, 2023

9.Insulin Resistance Alert: A Comprehensive Review of Its Hazards — Current Research in Diabetes & Obesity Journal, 2025

Note: This post is for informational purposes and reflects current scientific literature. It does not constitute medical or nutritional advice. Always consult a qualified health professional for guidance specific to your child or your own health.