Ultra-Processed Food, the gut, and performance: What you should know
- Mary Brooking
- Nov 12
- 5 min read
Reading Chris Van Tulleken’s book “Ultra-Processed People” changed the way I eat and think about food, and I have given it and recommended it (probably boringly and at length, sorry) to many people. More about the book is below but its subtitle gives a good steer to its contents “Why do we all eat stuff that isn’t food… and why can’t we stop?”
What is Ultra Processed Food (UPF)?
The book characterises UPF as “Ultra-processed food is not really food. It’s an industrially produced edible substance designed to be convenient, affordable and irresistible.”
It states that typically they:
are manufactured using industrial techniques and multiple-step processes (e.g., extrusion, moulding, pre-frying) rather than simple home cooking.
include ingredients that you would not commonly use in home cooking e.g. hydrogenated oils, high-fructose corn syrup, modified starches, protein isolates, artificial flavourings, emulsifiers, etc.
tend to be energy dense, low in fibre & low in micronutrients compared to unprocessed/minimally processed foods.
are often designed to be convenient, have a long shelf‐life and highly palatable which can lead to overconsumption.
And also: “When you eat an ultra-processed diet, you’re eating something that has been engineered to make you eat more of it.”
Gut feeling
I’d never thought about UPF in the context of exercise and endurance performance until I read an article this week that shone a spotlight on this for me in Runner’s World magazine (Gut Feeling: What is the gut microbiome and why is it important for runners by Renee McGregor). This sets out that there is increasing research that not only does exercise favourably influence our gut microbiome but also our gut microbiome can positively influence our endurance, with evidence of different specific gut microbiome characteristics being linked to each of a high/improving VO2max (ie aerobic capacity or endurance) and an elevated lactate threshold (ie anaerobic capacity or sustaining intense efforts). Additionally a healthy gut microbiome plays a crucial role in supporting mitochondrial health, essential for converting the dietary fuel we consume into muscle energy.
But what factors can harm our gut microbiome?
One key thing is ingredients commonly found in UPF food such as emulsifiers. What does this mean we should do about sports nutrition products such as gels, bars and recovery shakes, most of which are UPF? By ensuring high fibre choices (wholemeal bread and pasta, beans, fruit & veg) around your consumption of UPF you can mitigate the worst consequences of these products. You can also effectively train your gut to tolerate “real food” while exercising although that is a lot more difficult as intensity and duration of exercise increase, meaning gels become the only realistic option for some events.
It’s important to also say that extreme exercise, especially if accompanied by insufficient recovery can result in dysbiosis (when the balance of good bacteria in the gut microbiome is overridden by less beneficial bacteria). Similarly, low energy availability relative to exercise requirements, specifically low carbohydrate intake, can also cause dysbiosis, affecting not only performance but also the absorption of key nutrients such as iron.
“I think the UPF debate is interesting and needs a bit more nuance - doesn't
everything! I think a lot of the "bad" of UPF actually aligns to general nutritional guidance - eat less salt, fat and more fibre. But I think generally they should be a very small proportion of your diet - where you really need the logistical or convenience benefit. With a huge emphasis on really!”
Rebecca: Eat Well Perform Better
My thanks go to Rebecca for her thoughts and comments on this article, particularly the view that not all UPF is equally bad, and we should be thinking harder about which have the most negative impacts. I’m looking forward to working with Rebecca again in January’s Run Foundations course and she’s also got her marathon nutrition online course starting again early in 2026. I found it really useful, and definitely changed my pre-run and pre-race nutrition as a result.
Some ideas for performance fuelling with real food were in an article from a couple of months back I wrote with Rebecca from Eat Well Perform Better and Becky from Mace Masters.
Ultra-Processed People: A deep dive into the book
UPFs are industrially formulated products—made from refined ingredients, chemicals and additives—designed to be hyper-palatable, cheap, and profitable.
They are “food-like” items built from ingredients that you’d never find in a home kitchen (e.g. emulsifiers, flavour enhancers, stabilisers).
Real food nourishes; UPF primarily stimulates—hitting pleasure centres in the brain without delivering genuine nutrition.
Processing changes how our body responds — even with identical nutrients
“You can have two diets with identical calories, fat, sugar and protein—but the one that’s ultra-processed will make you hungrier.”
Processing alters food structure—breaking down fibres, changing textures, and pre-digesting ingredients—so the body absorbs energy faster and fails to trigger normal satiety signals.
It’s not just what you eat—it’s how it’s made that determines how your body and brain respond.
“The processing changes how our bodies respond. The food is absorbed faster, our hunger hormones behave differently, and we stop recognising when we’ve had enough.”
Malnutrition in Abundance
“Ultra-processed diets can make you both overweight and undernourished at the same time.”
Because they are calorie-dense but nutrient-poor, people can consume excessive energy while still lacking vital vitamins, fibre, and minerals.
The body receives energy but not the building blocks it needs—creating a state of metabolic confusion: hunger persists despite overeating.
This explains why populations eating high levels of UPF experience both obesity and micronutrient deficiencies.
“We are surrounded by calories but starved of nutrition.”
UPFs dominate modern diets
“This is not a story about individual choice or weak willpower—it’s a story about industrial power.”
In the UK, roughly 60% of all calories come from UPFs; for children and lower-income groups, it’s closer to 80%.
Many foods that look and are even marketed as healthThis shift means that, for most people, real food is the exception, not the norm.
UPFs are cheaper, more shelf-stable, easier to distribute, and therefore disproportionately consumed by those with less time, money or access to fresh food.
“The purpose of these foods is not to nourish us, but to extract money from us.”
Implications - individual & society
“If you want to eat less UPF, start by noticing it. Once you see it everywhere, it becomes impossible to ignore.”
Individually start by increasing awareness of what you’re eating: reading ingredient lists (if it contains additives you wouldn’t cook with, it’s probably UPF), recognising additives, understanding how processing changes how our body responds, see what happens when you reduce UPF
Societal changes proposed include regulation of marketing and clearer labelling together with seeing food not just as a health issue but as having environmental, social justice and cultural dimensions.
Nuances & caveats
Van Tulleken acknowledges things are complex: not every processed food is equally bad, not all of the evidence is perfect, and individuals have very different lives, budgets and constraints.
He also points out that cooking fresh food takes time, money and resources that many don’t have.
Some critics say the definitions of UPF are broad and risk moralising what people eat, or inducing stress around diet, both unwanted outcomes.
An alternative viewpoint is that rather than demonising all UPF we should be thinking harder about which have the most negative impacts and how can they be avoided most effectively.
References:
Ultra-Processed People: Chris Van Tulleken
Gut Feeling: What is the gut microbiome and why is it important for runners by Renee McGregor (Runner’s World Dec 2025) https://www.runnersworld.com/uk/health/a43350627/the-gut-microbiome/
Rebecca from Eat Well Perform Better https://www.eatwellperformbetter.co.uk
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