![\"Close-up](\"https://drreinwald.com/wp-content/uploads/2026/09/zitat-hintergrund-gehirn.jpg\")
\n
Did you know?
\n\n\n\nThe brain has no pain receptors.
\n\n\n\nIt cannot hurt, and it does not signal a deficiency with pain either.
\n\n\n\nWhat hurts in headaches are the surrounding membranes, vessels, and muscles.
\nYou take a supplement. The capsule dissolves, the nutrient sets off on its journey. And then? Most people imagine it as a straight path: mouth, stomach, blood, brain. In reality, there are two checkpoints on this journey, and both are highly selective. First, the intestinal wall decides what gets into the body at all. Then the blood-brain barrier decides what is allowed into the brain.
\nMuch of what we consume for our head never gets there. Not because the amount is too small, but because the form is not right. This article explains how this selection works.
Your brain makes up about two percent of your body weight and uses around one fifth of your energy turnover. And, in terms of dry mass, it is built from about 60 percent fat.
This is not storage fat, but construction material. Your roughly 86 billion nerve cells do not sit in fat; their sheaths are made of it. Every thought, every memory, every stimulus runs through structures made of fat molecules. If you want to nourish your brain, you are nourishing fat structures.
What lipid layers actually are
\nEvery cell is surrounded by a membrane, and this membrane is a double layer of fat molecules: two rows of tiny matchsticks, with the water-loving heads facing outward and the water-repelling tails facing inward. In the middle lies a fatty zone through which nothing water-soluble can simply stroll.
In nerve cells, myelin is added, the insulating layer around the long extensions. It works like the coating of a cable. Both structures have the same characteristic: they allow fat-soluble substances to pass more easily than water-soluble ones. This one property explains almost everything that follows.
\nBefore a nutrient gets anywhere near your head, it has to pass through the intestinal wall. It is not an open door, but a highly selective boundary surface. What is not absorbed here leaves your body unused, no matter how much of it was listed on the label.
Your microbiome has a say
\nTrillions of microorganisms live in your gut, and they are not just accessories. They live on fiber that you cannot digest yourself and produce short-chain fatty acids such as butyrate for your intestinal mucosa. Some strains also produce B vitamins and vitamin K2. Antibiotics, chronic stress, and a one-sided diet throw this system out of balance. A fiber-rich, plant-focused diet is the simplest thing you can do for this first stop.
The gut-brain axis
\nThe gut and brain are not separate departments. They are directly connected via nerve pathways, above all the vagus nerve, as well as via messenger substances and immune signals. The gut has its own nervous system with more nerve cells than the spinal cord.
\nIt is well established that this connection communicates in both directions. Science is currently investigating how strongly it affects mood and concentration.
Did you know?
\n\n\n\nThe brain has no pain receptors.
\n\n\n\nIt cannot hurt, and it does not signal a deficiency with pain either.
\n\n\n\nWhat hurts in headaches are the surrounding membranes, vessels, and muscles.
\nThe intestinal wall does not have one door, but several. Which one a substance takes determines its further path.
\n\n\n\nSmall water-soluble molecules slip between the cells or are ushered in via transporters. Both routes lead into the portal vein, meaning first to the liver, which immediately converts part of the load again.
\n\n\n\nFat-soluble substances take a different route. Bile acids package them into tiny droplets, the micelles. The intestinal cell absorbs them and builds them into transport particles, which are first released into the lymph. Only from there do they enter the blood, bypassing the liver. For this, however, they need fat in the meal, which is why good supplements advise taking them with a meal containing some fat.
\n\n\n\n“As long as it gets into the blood” is therefore only half the story. For DHA and for fat-soluble vitamin C, this very detour via the lymph is the reason why they arrive intact where they are needed.
\n\n\n\n\n\n\n\n\n\n\n\nOnce a nutrient has passed through the intestine, it is in the blood. But that does not mean it is in the brain by any means.
\n\n\n\nThe blood-brain barrier is not an organ that could be dissected out. It is the entirety of the vessel walls in the brain: around 600 kilometers of the finest capillaries, whose cells lie so tightly together that practically nothing seeps through between them. Every molecule has to pass through the cells, not around them. This is exactly why your brain works so remarkably steadily: the barrier keeps fluctuations in the blood away from the most sensitive tissue in your body.
\n\n\n\n\n\n\n\nThere are essentially two ways in.
\n\n\n\nPassively, by diffusion. Small, fat-soluble molecules dissolve in the fatty layer of the vascular cells and migrate through. The smaller and more fat-soluble, the easier. As a rough guideline, a size below about 500 daltons applies.
\n\n\n\nActively, via transporters. There are specialized gates for essential water-soluble substances. Glucose enters via the GLUT1 transporter, independently of insulin; amino acids use their own systems. These gates recognize a specific molecular shape and take only that along.
\n\n\n\nEverything else stays outside. A look at pharmaceutical research shows just how consistent this is: according to the much-cited assessment by William Pardridge, more than 98 percent of all small-molecule substances fail at the blood-brain barrier (Pardridge, Neurotherapeutics 2005), even though they were specifically developed for the brain. The barrier is not picky; it is uncompromising.
\n\n\n\nFor you, this means: the crucial question is not how much of a nutrient is in the capsule. It is whether its form is an entry ticket at all.
\n\n\n