Key takeaways
  • Brain fog isn't a medical diagnosis; it's a catch-all term for cognitive problems like feeling foggy-headed or unable to concentrate.
  • The causes are varied and can include blood sugar fluctuations, lack of sleep, nutrient deficiencies, allergies or gluten sensitivity, artificial sweeteners and monosodium glutamate (MSG), and hormonal imbalances.
  • I recommend starting by reviewing your lifestyle habits — low‑GI eating, healthy fats, sleep, exercise, and hydration — and seeing whether temporarily eliminating any suspect foods makes a difference.
  • If symptoms persist, it's a good idea to get blood tests and see a specialist to check for thyroid problems, vitamin deficiencies, or lingering infections (for example, long COVID).

That "foggy-headed" feeling — What is brain fog?

We've experienced it too — sometimes our heads feel heavy, words won't come, and our decision-making feels sluggish. In the West this is called "brain fog" (ブレインフォグ: literally "brain mist"), and it's treated more as a cluster of symptoms than a distinct medical diagnosis. Clinical research on the autonomic nervous system also shows that brain fog is often observed in connection with autonomic function and overall systemic condition (Ross et al., 2013). There isn't a single medication that cures it, but in many cases symptoms improve once the underlying causes are identified and addressed.

Common Symptoms and Our Experiences

Typical symptoms

  • Decline in thinking and judgment; feeling mentally foggy.
  • Decreased concentration and becoming easily distracted after a short period of time.
  • Memory decline (can't recall words or appointments)
  • Difficulty finding the right words; decreased work efficiency.
  • It can be accompanied by fatigue and low mood.

What we learned from trying it

For example, when we experienced strong sleepiness and a drop in concentration in the afternoon, we cut back on carbs at lunch and focused on protein and vegetables, and the afternoon “haze” eased considerably. Honestly, the cause is often not just one thing, and combining several measures tends to be more effective.

Top 10 Causes of Brain Fog and Practical Ways to Address Them

Here we’ll outline commonly reported causes and specific, practical steps you can start taking today (in no particular order).

1. Rapid blood sugar fluctuations (sugar and refined carbohydrates)

When excessive carbs cause your blood sugar to spike and crash, the brain can easily end up short on energy. To counter that, switch to low‑GI meals, cut back on bread or white rice at lunch, and choose snacks like nuts or cheese. When we made lunch mainly protein and vegetables, our afternoon concentration improved.

2. Inappropriate fat intake (too little fat / insufficient omega-3s)

Our brains are organs rich in lipids. It’s important that we include moderate amounts of good fats (EPA/DHA from fatty fish, avocado, olive oil, coconut, etc.) in our diets. Avoid extreme low‑fat diets. Neuroscience research has shown that essential fatty acids are important for brain function (Chang et al., 2009).

3. Lack of sleep and reduced sleep quality

Sleep is essential for restoring cognitive function. Let’s improve sleep quality by cutting blue light before bed, keeping a consistent sleep rhythm, and getting short bouts of exercise or sunlight during the day. Aim for about 7–9 hours.

4. Nutrient deficiencies (vitamin B12, iron, vitamin D, folate, etc.)

These deficiencies can cause fatigue and reduced concentration. Get a blood test to check, and if needed discuss supplementation with your doctor. Be especially mindful if you're vegetarian or currently dieting.

5. Allergies and Food Intolerances (including gluten)

Wheat gluten and other food allergens can sometimes cause physical symptoms and brain fog. It can be helpful to eliminate suspected foods for 2–3 weeks to see how you feel, or to undergo allergy testing. Books like Grain Brain also address the effects of wheat, but keep in mind there is considerable individual variation.

6. Artificial sweeteners and monosodium glutamate (MSG)

Artificial sweeteners and MSG have been reported to be linked, in some people, to brain fog, headaches, and trouble concentrating. If you often consume them in processed foods or when eating out, try cutting back for a few weeks and see if you notice any changes.

7. Stress and Chronic Inflammation

Long-term stress and chronic inflammation can impair cognitive function. We can help relieve stress with mindfulness, deep breathing, gentle exercise, and social activities.

8. Hormonal imbalances (thyroid, female hormones, etc.)

Hypothyroidism and the hormonal changes of menopause can cause brain fog. I recommend getting blood tests and consulting with an endocrinologist.

9. Medication side effects and chronic infections (long-term infections)

Some medications and chronic conditions (for example, lingering post-COVID-19 symptoms) can cause brain fog. Please talk with your doctor about reviewing your medications and treatment plan.

10. Lifestyle habits (dehydration, lack of exercise, excessive screen time)

Even mild dehydration can cause slight cognitive impairment. Regularly sipping water and taking short walks or stretches to get the blood flowing are effective. When doing screen work, take frequent breaks — techniques like the Pomodoro Technique make it easier to regain focus.

Everyday Self‑Care (Simple Habits You Can Try Right Away)

Eating Tips

- For breakfast, combine protein, healthy fats, and low-GI carbohydrates. - Cut back on processed foods, excess sugar, artificial sweeteners, and MSG. - Get omega-3s from oily fish, flaxseed, and chia seeds.

Sleep · Exercise · Rest

- Go to bed and wake up at the same time every day. - Getting morning sunlight makes it easier to regulate your circadian rhythm. - Do aerobic exercise and strength training a few times a week to improve blood flow.

How we think about tests and supplements

- If symptoms persist, have blood tests (thyroid, vitamin B12, iron, vitamin D, etc.). - It's safest to take supplements only after consulting your doctor and confirming a deficiency.

Work and Environment Tips

- Regain your focus with the Pomodoro technique (25 minutes work + 5-minute break) - Set up your workspace and turn off unnecessary notifications

Summary

Brain fog—literally “a mist in the brain”—can happen to anyone, and its causes are complex rather than single. The quickest path to improvement is to get the basics in order: diet (blood sugar control and quality fats), sleep, exercise, hydration, and stress management. When we actually tried this, we noticed clear improvements by cutting back on carbohydrates at lunch and focusing on protein, and by giving up artificial sweeteners. That said, if symptoms are severe or persistent it’s important to get blood tests and see a specialist to properly identify the cause. Let’s start with small lifestyle tweaks and gradually clear the fog in our heads.

Disclaimer: The information in this article is for general informational purposes only and does not constitute medical advice. Please consult a qualified healthcare professional before making any health-related decisions.