Why do you have brain fog, even though you eat well and exercise?

A woman with fog around her brain depicting "brain fog".

You eat your greens, stay active, usually reach your protein target. But you’re still left wondering, “why is my brain so foggy?”.

Do you lose your train of thought mid-sentence?

Do tasks take longer than they should because you’re so distracted?

Do you find yourself in a room knowing you went to do something but can’t remember what?

What is happening? Is it normal to feel this way even when you’re living a healthy lifestyle? Let’s take a look at some of the most common (and often overlooked) reasons behind brain fog in active, health-aware people like you.

Does Your Diet Affect Your Brain Health?

In short… yes, and much more than most people realise.

Your brain is small (no offence intended), but very greedy! Although it makes up only 2% of your body weight, it uses approximately 20% of your daily energy intake. It relies on a steady supply of specific vitamins, fats, and phytonutrients to function well day to day, and to stay sharp as you age.

Without the right nutrients, your brain cells can quite literally run low on energy and lack the tools to function properly. Especially if they’re struggling to use glucose efficiently, which may happen with age, chronic stress, or insulin resistance. That’s when you might start experiencing cognitive symptoms like brain fog, forgetfulness, and sugar cravings.

Here are some of the nutrients that play a major role in supporting brain health:

Omega-3s (especially DHA): DHA is a key constituent of a healthy brain structure and often in short supply in a modern diet. Without these essential fats, your neurons will struggle to communicate efficiently. Oily fish is the richest source — aim to regularly include salmon, mackerel, anchovies, sardines, herring (S.M.A.S.H). Algae is a rich plant source.
Phospholipids: Making up over half of the brain cell membrane, phospholipids are the structural foundation of healthy brain cells. Dietary sources include egg yolks, organ meat, herring and soybeans.
B Vitamins (especially B6, B12, folate): B vitamins are needed for energy production and to make the brain cell membrane. They are also essential for neurotransmitters, the chemical messengers your brain uses for brain function and mood regulation. B vitamins are found in leafy greens, while B12 tends to come from animal sources like meat, seafood, eggs, and dairy.

Fish being stuffed with herbs on parchment paper ready to bake.

Interesting note:

Research shows that B vitamins and omega-3s work even better together. By helping to reduce oxidative stress in your brain cells and support mitochondrial energy production, cognitive function was better supported.

Polyphenols: Found in colourful plant foods, antioxidant phytonutrients such as anthocyanins can reduce inflammation and protect your brain from damage. The more variety in colour, the more you’ll naturally support your brain’s defences.
Magnesium: Magnesium supports nerve function, reduces inflammation and protects the brain which supports memory, learning, and nervous system regulation. Include plenty of leafy greens, whole grains, nuts and seeds to increase your magnesium intake.
Choline: Needed to produce acetylcholine, choline is a neurotransmitter vital for memory and attention. Egg yolks are a fantastic source, but you can also get choline from organ meat, poultry, fish and some legumes.

Even with a “healthy” diet, it’s easy to fall short on one or more of these nutrients, especially if you’re eating the same meals on rotation, avoiding key food groups, or simply not eating enough to meet your needs.

Are You Eating Enough to Support Your Brain?

This is particularly relevant if you train regularly, lead an active lifestyle or are restricting calories to reduce body fat. Low energy availability (LEA) can become an issue when your food intake doesn’t match the energy your body needs, not just for training, but for all the other functions taking place behind the scenes, including but not limited to, cognitive function.

You may be eating a diet that looks very healthy, but if it’s not enough to cover both exercise and daily function, cognitive symptoms become likely. This can look like:

Impaired concentration and memory
Poor decision-making and slower reaction time
Reduced ability to handle training stress
Increased risk of low mood or less motivation

Symptoms of LEA are not confined to brain health. Ongoing LEA can disrupt hormonal balance, impact bone density, suppress immune function and affect gut health.

To prevent this, the obvious thing is to increase your calorie intake but focus on adding more nutrient dense carbohydrates such as root vegetables and whole grains. Women especially should focus on eating carbohydrates earlier in the day and before training is also helpful to signal to your brain that energy is present.

Why Do You Get Brain Fog After Eating Certain Foods?

There’s growing evidence that your gut and brain are closely connected, a relationship known as the gut-brain axis.

Certain foods, especially alcohol, sugar, and ultra-processed products, can disrupt the balance of bacteria in your gut. This includes many “health” or “sports” foods that contain additives known to affect the microbiome.

When the gut becomes inflamed, the gut wall can also become more permeable, sometimes referred to as “leaky gut.” This allows undigested food particles and toxins to enter the bloodstream, triggering immune responses and contributing to the development of food intolerances, which can further exacerbate cognitive symptoms.

The result? Even if your diet may appear healthy, food intolerances and ongoing gut inflammation can manifest as brain fog, forgetfulness, low mood, or poor focus, all signs that the brain isn’t functioning at its best.

What Should I Eat to Improve My Brain Function?

If you’re looking for better focus, sharper memory, and fewer flat, foggy days, these five simple dietary changes are a practical and effective place to start.

1. Eat oily fish three times a week

Many diets fall short of the omega-3 fats that are essential for brain structure and mood regulation.

Try this: Add salmon, sardines, mackerel or anchovies to your weekly meals. If you are vegan, look for algae-based DHA supplements.

2. Prioritise leafy greens and colourful plants

These are packed with B vitamins, magnesium and polyphenols, nutrients that reduce inflammation and support energy production in the brain.

Try this: Aim for one portion of leafy greens and at least 5 different plant colours each day.

3. Don’t under-fuel, especially around training

Low energy availability can impair memory, focus and recovery. Your brain needs fuel just as much as your muscles do.

Try this: Include a source of nutrient dense carbohydrate (from root vegetables and whole grains) at each meal. Aim to eat carbohydrates earlier in the day and around intense activity, particularly if you are female.

4. Focus on real food over processed options

Even “healthy” sports foods can contain additives that affect gut health, and through the gut-brain axis, your mental clarity too.

Try this: Prioritise whole food snacks like boiled eggs, apple with nut butter, or leftovers, instead of bars or powders. If you do use protein powders, check the ingredients to avoid additives.

5. Don’t skip the yolks

Eggs, especially the yolks, are rich in choline and phospholipids, both of which are essential for memory, focus, and maintaining healthy brain cell structure.

Try this: Include whole eggs a few times a week - boiled, poached, or added to meals. They're quick, affordable, and one of the most nutrient-dense foods for your brain.

Final thoughts

Brain fog is surprisingly common, even in active, health-focused people. But the good news is, a few simple dietary shifts can make a real difference, helping your brain get the fuel and nutrients it needs to think clearly, focus better, and feel more like you.

If your current approach isn’t delivering the clarity and focus you’d expect, it may be time to take a closer look. You can join the Performance Plate Audit Priority List to be the first to know when this launches, or arrange a call to explore what could be affecting your brain function.