Food intolerances and sensitivities are often confusing. Some people seem to tolerate everything without issue, while others experience bloating, headaches or fatigue after certain meals – and for many, these reactions can appear suddenly, even after years of eating the same foods without a problem.
So why do food sensitivities develop? Here's a closer look at the science behind them.
The Role of Genetics
In some cases, genetics play a genuine role:
- Enzyme deficiencies – adult lactose intolerance, for example, is linked to a genetic reduction in the enzyme lactase. Without enough lactase, the body struggles to digest lactose, leading to cramps, bloating or diarrhoea.
- Inherited tendencies – some families are more prone to certain intolerances or sensitivities, though environment and lifestyle also play a part.
Genetics may set the foundation, but they're rarely the only factor.
Environmental and Lifestyle Factors
Surroundings and habits can also shape how the body reacts to food:
- Antibiotic use – can disrupt gut microbiome balance, sometimes contributing to new intolerances or sensitivities.
- Dietary patterns – highly processed foods, artificial additives, or low-fibre diets may place more strain on digestion, potentially increasing the risk of intolerance.
- Environmental exposures – ongoing exposure to pollution and certain chemicals may add to the body's overall burden, potentially reducing tolerance to some foods.
Gut Health Changes
The gut plays a central role in many food reactions. When functioning well, it digests food and absorbs nutrients efficiently – when compromised, intolerances and sensitivities can become more likely.
- Increased intestinal permeability (sometimes referred to as "leaky gut") – a weakened gut lining may allow food particles to interact more directly with the immune system, potentially contributing to new sensitivities.
- Microbiome imbalances – reduced gut bacteria diversity can make the digestive system more reactive to certain foods.
- After illness or infection – temporary intolerances often develop following a stomach bug or gastroenteritis, and can improve as the gut recovers.
The Cumulative Effect
Sometimes intolerances don't stem from a single cause, but build up over time:
- Eating several moderate-reactivity foods in one day may cause symptoms, even if none would individually.
- Regular exposure to additives or highly processed ingredients can gradually reduce tolerance.
- Chronic stress and poor sleep can weaken digestion over time, compounding the issue.
When Do Intolerances and Sensitivities Develop?
Reactions can appear at any age:
- In childhood – some children are born with intolerances, such as lactose intolerance or sensitivity to soy or certain fruits. Many outgrow these as their digestive system matures.
- In adulthood – intolerances often develop later in life, sometimes following illness, stress, hormonal changes, or gradual enzyme decline. Lactose intolerance commonly first appears in the teenage years or adulthood.
- In older age – digestive efficiency often declines naturally with age, making older adults somewhat more prone to intolerances.
Links to Stress, Hormones and Digestion
The gut doesn't function in isolation – stress and hormones can directly affect digestion and tolerance.
- Stress – chronic stress can alter gut motility and reduce enzyme production, making digestion harder.
- Hormonal shifts – changes during puberty, pregnancy or menopause can influence gut function and sensitivity.
- The gut-brain connection – mood and digestion are closely linked, so stress, anxiety or low mood can all increase the likelihood of food reactions.
Bottom Line
Food intolerances and sensitivities can develop for many reasons – genetics, gut health, stress, environment, or simply natural changes with age. While they're not usually dangerous in the way allergies can be, they can have a real, ongoing impact on how you feel day to day.
Understanding your body's reactions is the first step toward feeling better. Supporting gut health, managing stress, and identifying trigger foods can help many people ease, or even prevent, uncomfortable symptoms.
If you regularly experience bloating, fatigue or headaches after eating, our Body Intolerance Test can help you understand what's going on – analysing 1,500 items from the comfort of home, helping you pinpoint your personal triggers and take back control of your wellbeing.
