Ultra-processed foods (UPFs) defined as industrial products made with artificial additives, refined carbs, trans fats, salt, sugar, and emulsifiers. These foods contribute to increased calorie intake and raise the risk of chronic diseases like type 2 diabetes, obesity, and mental health problems.

Studies show UPFs likely disrupt the gut microbiome by triggering inflammation and altering immune system responses. These changes can affect brain chemicals, increase inflammation, and reduce overall nutritional quality. Several studies also link additives and contaminants in UPFs to poor metabolic health, consistently showing that UPFs negatively impact gut health and metabolism.

The Reward System

Foods that combine fat and sugar are more rewarding than those containing either macronutrient alone. Studies show that fat and sugar activate different gut-brain pathways, each releasing dopamine (the feel-good chemical) in the brain. When eaten together, they boost dopamine even more, intensifying the drive to eat more and promoting overeating.

Rodent studies suggest that this increased reward response may overpower interoceptive signals (internal cues that help regulate hunger and satiety) potentially reducing cognitive control over eating behaviour, even in individuals actively trying to diet. This means that eating less food high in both fat and sugar could help you stay more aware of your body's hunger signals and make healthier eating choices. More research is needed in this area to fully understand the direct links in humans.

Stress and frequent UPF consumption may activate the brain’s reward system, reinforcing unhealthy eating patterns and increasing the risk of depression. Studies show that every 10% increase in UPF intake was linked to a 21% higher risk of depression. However, most of this evidence comes from observational studies, which cannot confirm cause and effect.

Changes in Eating Behaviours

UPFs influence eating behaviours, often leading to skipped meals, irregular eating patterns, and the replacement of nutritious foods with high-calorie alternatives. Skipping meals, especially breakfast, can impair blood sugar control and make it harder to maintain stable glucose levels throughout the day.

UPFs not only affect physical health but also reshape eating behaviours in ways that undermine metabolic stability. Frequent consumption of UPFs has been linked to disrupted appetite regulation, often leading to skipped meals, irregular eating patterns, and a tendency to replace nutrient-dense foods with high-calorie, low-nutrient alternatives. These behavioural shifts are partly driven by how UPFs interact with the brain’s reward system, overstimulating hunger and satiety circuits and reinforcing cravings even in the absence of true hunger.

Skipping meals, particularly breakfast, can lead to elevated mean blood glucose levels throughout the day and reduce the body’s ability to respond effectively to insulin. This is especially concerning for individuals at risk of or living with type 2 diabetes, as irregular eating patterns combined with high UPF intake may exacerbate insulin resistance and increase HbA1c levels over time.

Moreover, the convenience and palatability of UPFs often encourage grazing or binge-like eating behaviour rather than structured meals, further destabilising blood sugar regulation. Over time, this cycle of irregular eating and metabolic disruption can contribute to obesity, mood disorders, and chronic disease progression.

Eating Out vs Homemade

Research shows that eating out, particularly consuming fast food and ready-made meals is associated with significantly higher intake of added sugars and refined starches compared to meals prepared at home. These foods often rely on low-cost, highly processed ingredients that are energy-dense but nutrient-poor. For example, fast food items like burgers, fries, and sweetened beverages are typically high in rapidly digestible carbohydrates, which can cause sharp spikes in blood sugar levels. Ready-made meals, while convenient, often contain hidden sugars and refined starches to enhance taste and shelf life, contributing to excessive calorie intake without providing sustained satiety or fibre.

In contrast, home-cooked meals tend to include more complex carbohydrates such as whole grains, legumes, and vegetables which digest more slowly and help regulate blood sugar. The glycaemic index (GI) of many fast food and ready-made items is considerably higher than that of minimally processed foods, meaning they can lead to quicker rises in blood glucose and insulin levels. Over time, this pattern of eating may increase the risk of insulin resistance, type 2 diabetes, and weight gain.

Moreover, socioeconomic and time constraints often drive reliance on convenience foods, reinforcing a cycle of poor dietary quality and health outcomes. Encouraging home cooking and improving access to affordable, whole-food options are key strategies for reducing excessive sugar and starch intake from eating out.

Key Takeaways

• UPFs are high in unhealthy fats, sugars, and salt, increasing the risk of obesity, type 2 diabetes, and mental health issues.

• UPFs disrupt the gut microbiome, trigger inflammation, and negatively affect metabolism.

• Foods combining fat and sugar are especially rewarding to the brain, promoting overeating and making it harder to control eating habits.

• Frequent UPF consumption is linked to irregular eating patterns, skipped meals, and replacing nutritious foods with calorie-dense, nutrient-poor options.

• Skipping meals, especially breakfast, impairs blood sugar control and increases insulin resistance, particularly in those at risk for diabetes.

• Eating out (fast food, ready-made meals) can lead to higher intake of added sugars and refined starches, causing blood sugar spikes and increasing disease risk.

• Socioeconomic and time pressures drive reliance on UPFs, but encouraging home cooking and access to whole foods can improve health outcomes.