A greasy takeaway may seem like an innocent Friday night indulgence. But our recent research suggests even a single high-fat meal could impair blood flow to the brain, potentially increasing the risk of stroke and dementia.
Authors
- Chris Marley
Senior Lecturer in Exercise Physiology, University of South Wales
- Damian Bailey
Professor of Physiology and Biochemistry, University of South Wales
Dietary fat is an important part of our diet. It provides us with a concentrated source of energy, transports vitamins and when stored in the body, protects our organs and helps keep us warm. The two main types of fat that we consume are saturated and unsaturated (monounsaturated and polyunsaturated), which are differentiated by their chemical composition.
But these fats have different effects on our body. For example, it is well established that eating a meal that is high in saturated fat, such as that self-indulgent Friday night takeaway pizza, can be bad for our blood vessels and heart health. And these effects are not simply confined to the heart.
The brain has limited energy stores, which means it is heavily reliant on a continuous supply of blood delivering oxygen and glucose to maintain normal function.
One of the ways the body maintains this supply is through a process known as "dynamic cerebral autoregulation" . This process ensures that blood flow to the brain remains stable despite everyday changes in blood pressure, such as standing up and exercising. It's like having shock absorbers that help keep our brains cool under pressure.
But when this process is impaired, those swings in blood pressure become harder to manage. That can mean brief episodes of too little or too much blood reaching the brain. Over time, this increases the risk of developing conditions like stroke and dementia.
What role might diet play?
After eating a meal high in saturated fat, levels of fat in the blood rise and peak after around four hours. At the same time, blood vessels become stiffer and lose their ability to relax and expand. This restricts blood flow around the body. But little is known about what happens to the brain during this time and how well its blood supply is protected.
To address this for the first time, we recruited 20 young men between the ages of 18 and 35, and 21 men between 60 and 80. We measured how well blood vessels linked to heart and brain health worked before, and four hours following, consumption of a meal high in saturated fat.
We assessed how well a blood vessel in the arm could open up in response to increased blood flow to obtain an indication of heart health. This is a method known as "flow-mediated dilatation" .
To evaluate how well blood vessels in the brain could cope with swings in blood pressure, our participants performed body-weight squats. We used ultrasound to determine how well blood flowed through vessels during both methods.
The test meal was a milkshake, which we called "the brain bomb" because it consisted mostly of heavy whipping cream. The drink contained 1,362 calories and 130g of fat, mimicking the fat load of a fast-food takeaway.
Our findings confirmed previous research that has shown that a high-fat meal impairs the ability of the blood vessels linked to heart health to open in both young and old participants. These impairments reduced the brain's ability to buffer changes in blood pressure. This was more pronounced (by about 10%) in the older adults, suggesting that older brains may be more vulnerable to the effects of the meal.
Although we didn't directly test for the long-term effects of a high-fat meal on mental functioning in this study, we have previously shown that such a meal increases free radicals (unstable, cell-damaging molecules) and decreases nitric oxide (molecules that help blood vessels relax and open up to transport oxygen and glucose around the body).
This may explain the reduced blood flow regulation we observed in our recent study.
This has important clinical implications. While an occasional takeaway is unlikely to cause harm on its own, our results suggest that even one fatty meal has an immediate effect on the body.
Our study highlights the importance of consuming a diet that is low in saturated fat to protect not only our heart health, but also our brain health. This is particularly important for older adults whose brains appear to be more vulnerable to the effects of such a meal and are already at increased risk of stroke and neurodegenerative diseases.
The NHS recommendeds that men consume no more than 30g of saturated fat a day, while women should consume no more than 20g. Yet many of us routinely exceed that, particularly during weekend takeaways, pub lunches or fast-food splurges.
What's more, we may spend much of our waking lives in a post-meal state. This period, known as "post-prandial lipaemia" , is when fat levels are elevated, and when the body, it seems, may be most at risk.
Food for thought
There's still so much more we need to learn about this topic.
Public health guidance recommends swapping saturated fats for polyunsaturated ones. These are found in foods like oily fish, walnuts and seeds, which are associated with better heart and brain health over the long term. But we don't yet know how the brain responds to a single meal that is high in polyunsaturated fat.
Nor do we know how the female brain responds to a high-fat meal. This is a crucial gap in our knowledge since women face a greater risk of stroke and dementia in later life compared to men.
Our study offers a timely reminder that diet doesn't just shape our long-term health. It also affects our body and brain in real time. And as we're learning, when it comes to protecting brain health, every meal may count.
D.M.B. is supported by a Royal Society Wolfson Research Fellowship (Grant No. WM170007). D.M.B. is Editor-in-Chief of Experimental Physiology, Chair of the Life Sciences Working Group, member of the Human Spaceflight and Exploration Science Advisory Committee to the European Space Agency, member of the Space Exploration Advisory Committee to the UK and Swedish National Space Agencies and member of the National Cardiovascular Network for Wales and South-East Wales Vascular Network. D.M.B. is also affiliated to Bexorg, Inc. (USA) focused on the technological development of novel biomarkers of cerebral bioenergetic function and structural damage in humans.
Chris Marley does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
