L8 - Ultra-processed diet and health outcomes

Describe the 4 levels of food processing and give an example of each level

• Group 1 - unprocessed or minimally processed foods. Processing includes removal of inedible/unwanted parts and does not add substances to the original food, e.g., fresh, dry or frozen vegetables or fruit, grains, legumes, meat, fish, eggs, nuts and seeds

• Group 2 - processed culinary ingredients. Substances derived from group 1 foods or from nature by processes including pressing, refining, grinding, milling, and drying, e.g., plant oils, animal fats, maple syrup, sugar, honey, and salt

• Group 3 - processed foods. Processing of groups 1 or 2 with the addition of oil, salt, or sugar by means of canning, pickling, smoking, curing, or fermentation

• Group 4 - ultra-processed foods. Formulations made from a series of processes including extraction and chemical modification. Includes very little intact group 1 foods, e.g., sugar-sweetened beverages, sweet and savoury packaged snacks, reconstituted meat products, pre-prepard frozen dishes, canned/instant soups, chicken nuggets, ice cream

What was the problem addressed by the study by Hall et al. (2019)?

Increased availability and consumption of ultra processed foods have been associated with rising obesity prevalence

What was the knowledge gap addressed by Hall et al. (2019)?

• Scientists have not yet demonstrated that ultra-processed food causes obesity or adverse health outcomes

• First study to address the causal role of ultra-processed foods on energy intake and body weight change

What was the aim of the study by Hall et al. (2019)?

To address the causal role of ultra-processed foods on energy intake and body weight change

What was the study setting?

In-patient setting in a hospital

What was the inclusion criteria?

• 18-50 years old

• BMI greater than 18.5 kg/m²

• Stable weight - less than ± 5% change over the past 6 months

What was the exclusion criteria?

• Medical conditions - anaemia, diabetes, cancer, thyroid disease, eating disorders or other psychiatric conditions

• Dietary restrictions - strict dietary concerns including food allergies or adherence to particular diets, e.g., vegetarian or vegan

What was the study design?

A randomised control trial where half of the participants had a 2-week ultra-processed diet and then a 2-week unprocessed diet and the other half had a 2-week unprocessed diet and then a 2-week ultra-processed diet

What was the primary outcome measure?

Energy intake measured as ad libitum (unlimited) energy intake

What were the secondary outcome measures? (3)

• Appetite and sensory assessment - subjective assessment of appetite, sensory and palatability

• Body weight and composition

• Blood biomarkers - assessment of appetite and metabolism

Describe the 14-day dietary intervention

• Exposure to an ultra-processed diet or an unprocessed diet for 14 days each

• Three meals per day unlimited access to snacks

• Autonomy over portion sizes - participants could eat as much or as little food as they wanted

Why were participants blinded to their weight?

• To reduce bias and behavioural changes

• If participants knew they were gaining or losing weight, they might consciously alter their eating habits, confounding the results

How were the 2 diets matched?

Diets were designed to be matched for presented calories, energy density, macronutrients, sugar, sodium, and fibre

What was the probability (power) and type 1 error probability of the study?

Power = 0.8

Type 1 error probability = 0.05

What were the results of the study with energy and nutrient intake and weight? (3)

• Ultra-processed diet significantly increased energy intake by about 500 kcal/day

• Ultra-processed diet significantly increased intake of carbohydrates and fat, but not protein which remained stable

• Ultra-processed diet caused significant weight gain (+ 0.4 +/1 0.1 kg) compared to the unprocessed diet (-0.3 ± 0.1 kg)

What were the results of the study with appetite? (2)

• PYY (an suppressing hormone) increased after the unprocessed diet compared to the ultra-processed diet and baseline

• Ghrelin (a hunger hormone) decreased after the unprocessed diet compared to the ultra-processed diet and baseline

What were the results with eating rate?

There was a significantly faster eating rate for ultra-processed meals

What were the conclusions of the study? (3)

• Eliminating ultra-processed foods from the diet decreases energy intake and led to weight loss

• A diet with a large proportion of ultra-processed foods increased energy intake and led to weight gain

• Limiting consumption of ultra-processed foods may be an effective strategy for obesity prevention

What were the strengths of the study? (3)

• In-patient experimental approach - controlled conditions and close monitoring

• Cross-over study design - reduces variability by having participants serve against their own controls

• Depth, detail and rigour of analyses - ensured comprehensive and thorough evaluation

What were the limitations of the study? (3)

• No washout periods between diets - could have led to carryover effects

• Relatively short-term study - limits the ability to assess long-term effects

• In-patient setting - results may not be generalisable as conditions do not reflect typical real-world settings

Why does this research matter for public health?

• Addresses a major public health issue - the role of ultra-processed foods on obesity

• Provides causal evidence under controlled conditions, informing dietary guidelines and policy

Would the same effects be seen under free-living conditions?

• Effects likely persist but magnitude may differ

• Free-living conditions introduce factors like cost, convenience, food environment and social influences that could amplify or reduce the effect

• Adherence and choice variability may dilute the impact compared to in-patient settings

Who do these findings apply to and who may they not apply to?

• They apply to adults aged 18-50 with a BMI above 18.5 kg/m²

• May not apply to children, older adults, or those with very high or low BMI

• Cultural and socioeconomic differences could influence outcomes