Chris Miller MD and I went deep on this one. We sat down for a Friday live and covered something that gets overlooked in the constant noise about macronutrients, protein targets, and which diet trend deserves your attention this week. We talked about the micronutrients that actually keep your brain and body running, the ones most people never test for, and what happens when they quietly fall short.

If you watched the replay, this is your reference guide. If you haven’t watched yet, start with the video above and come back here for the details.

Your Brain Has a Bouncer

Before we got into specific nutrients, Dr. Miller explained something worth understanding: the blood-brain barrier. Your brain is picky about what it lets in. Unlike your gut lining, which is one cell layer thick and held together by tight junctions, the blood-brain barrier is roughly 400 times tighter. It has to be. Your bloodstream carries immune cells, toxins, and pathogens that would cause serious damage if they reached your brain tissue.

Specialized cells called astrocytes, pericytes, and microglia wrap themselves around the blood vessels that supply the brain, creating a filtration system that only allows through what the brain actually needs: glucose via dedicated transporters, oxygen, carbon dioxide, and select nutrients. Everything else gets turned away.

When this barrier is working well, the brain stays protected while the glial cells on the inside handle cleanup and maintenance. That is a healthy brain. And the nutrients that make it through that barrier are exactly the ones we spent the rest of the session talking about.

Vitamin D

Dr. Miller started here because it is one of the most common deficiencies she sees, regardless of diet. You may not feel it right away, but signs can include slower wound healing, getting sick more often, autoimmune flares, and declining bone density.

The test to ask for is a 25-hydroxy vitamin D level. I aim to get my patients into the 40 to 60 range. Below 20 is clearly deficient, and most physicians will agree with that. Research during the pandemic showed that individuals with levels closer to 46 to 50 had less severe infections, which tracks with what we know about vitamin D’s role in immune and cardiovascular protection. It functions more like a hormone than a simple vitamin, and your whole body depends on it.

Here is the thing that surprised me about my own levels. I have lived in sunny places for most of my life. I run outside regularly without sun protection (yes, I know). And I have never been able to get my vitamin D above 30 without supplementation. There are genetic variations that affect your ability to convert sunlight into usable vitamin D, which is why testing matters more than assumptions.

Most of my patients do well on around 2,000 IU daily, but this is individual. I would not take over 4,000 IU without a physician monitoring your levels, because toxicity is real. NatureMade is a reliable, affordable brand you can find at any pharmacy or Walmart.

Magnesium

This one comes up constantly. Even people eating a solid plant-based diet can fall short. The challenge with magnesium is that blood tests are unreliable. Only about 1% of your total magnesium circulates in your blood, so a serum level can look normal while your tissues are depleted. An RBC (red blood cell) magnesium test is somewhat better, but still imperfect.

Pay attention to symptoms: muscle cramps, especially if you are on a diuretic like hydrochlorothiazide. Difficulty sleeping. Muscle twitching. Anxiety. Heart palpitations. Migraines. Headaches. Constipation. As we get older, the cramping and sleep disruption tend to be the most common complaints.

For food sources, pumpkin seeds are a powerhouse. I eat them every single day. Dark chocolate (you are welcome), avocado, almonds, and leafy greens are all solid sources. But if you have gut issues, if you are gassy or bloated or dealing with loose stools or constipation, there is a good chance you are not absorbing well. Aging also reduces stomach acid, which compounds the problem.

Someone asked during the live what the best form of supplemental magnesium is for muscle twitching. Dr. Miller and I both recommend magnesium glycinate (or bisglycinate), 200 to 400 milligrams. It absorbs well and is less likely to cause the GI side effects you might get from other forms.

Omega-3 Fatty Acids

Dr. Miller brought this one up because of her focus on inflammation and healthy aging. What your body really needs are EPA and DHA, the two omega-3 fatty acids that do the heavy lifting for joint health, cardiovascular protection, and brain function. DHA in particular is critical for the brain, and people who carry the APOE4 gene may need even more of it to get adequate amounts across the blood-brain barrier.

If you eat fatty fish like salmon, mackerel, anchovies, sardines, or herring, you are getting pre-made EPA and DHA. If you eat plant-based, you can get ALA from flax seeds, chia seeds, walnuts, hemp seeds, and leafy greens, and your body can convert that ALA into EPA and DHA through a series of enzymatic steps.

But not everyone converts efficiently. Research suggests that a meaningful percentage of the population has genetic variations that reduce this conversion. If your levels are low despite eating ALA-rich foods, you may need a direct source of EPA and DHA. Both Dr. Miller and I recommend algae-based omega-3 supplements for this reason. The fish get their omega-3s from algae anyway, so you are just cutting out the middleman.

I check an omega-3 index and aim for at least 5.5, though above 8 is probably ideal for cardiovascular health. Vitamin D, B12, and algae-based omega-3s are the three supplements I recommend nearly everyone consider. I like Nordic Naturals for the algae omega-3.

Vitamin B12

This is the non-negotiable one. If you eat a plant-based diet and you are not supplementing B12, stop what you are doing and start. B12 only comes from bacteria. Animals accumulate it because they consume bacteria through their food, and it gets stored in muscle tissue. Humans have bacteria that produce B12 in the gut, but it is made beyond the point of absorption. So you cannot rely on internal production.

The majority of my patients need 500 to 1,000 micrograms daily. And this is not only a plant-based issue. People taking metformin, proton pump inhibitors, or anyone getting older can have reduced B12 absorption regardless of diet.

Symptoms can be insidious. Numbness. Fatigue. Brain fog. Balance issues. I had a patient who had been vegetarian for most of her life and came to me in her mid-30s with severe nerve weakness, fatigue, and an inability to grip a cup without dropping it. Multiple doctors had missed it. Her B12 was below the low end of normal. We started injections, and within weeks, her grip strength returned. She was fortunate that she did not have permanent nerve damage, but that outcome is possible when deficiency goes unaddressed for too long.

I check three things: serum B12, homocysteine, and methylmalonic acid. I aim for a serum B12 above 500, and I want homocysteine below 10. I have seen homocysteine drop beautifully with B12 supplementation, even when the B12 level was technically in the normal range. Do not wait for a number to fall below the reference range before you act. That reference range represents 95% of the population, not necessarily what is optimal for you.

Iron

Iron deficiency deserves careful attention, especially for women. You can have normal circulating iron and normal iron saturation and still have low ferritin, which is your iron storage protein. That low ferritin can cause restless legs, sleep disruption, fatigue, brittle hair and nails, and hair loss. Research shows that people who replenish ferritin to at least 50 notice improvements in energy and focus. Sleep specialists prefer levels closer to 70.

Women who menstruate, endurance athletes, and runners are at higher risk. I know from experience. As I entered perimenopause, my periods got heavier and lasted longer. I was running longer distances. I was compounding the problem. And if you drink a lot of tea with meals, the tannins can reduce iron absorption, so separating tea from meals can help.

Pumpkin seeds are a great plant-based source, along with dark green leafy vegetables and beans. If you eat animal products, you are likely getting enough. But if you are supplementing iron, please do so under physician guidance. Too much iron causes its own set of problems. And if you are a man with low iron, that is unusual enough to warrant investigation. In my practice, low iron in men is rare, and when it does occur, we need to look for a source of loss, particularly GI bleeding.

Zinc

Zinc is a cofactor for nearly every cellular function in the body. Immune support, wound healing, thyroid function, and hair health all depend on it. Research shows that supplementing zinc within the first 24 to 48 hours of a cold can reduce the duration by a day or two.

You can test serum zinc, ideally in the morning since levels fluctuate throughout the day. Pumpkin seeds and cashews are excellent plant-based sources. Dr. Miller and I both see patients whose zinc remains low even after dietary changes, and those individuals need supplementation.

One important caution: high-dose zinc can interfere with copper absorption. If you stay under 10 to 15 milligrams of supplemental zinc, copper is generally not a concern. Above that, you want to be mindful.

Iodine

This is the one that sneaks up on people who are trying to eat healthier. Iodine comes primarily from seafood and iodized salt. When people clean up their diet, cut back on processed foods, switch to sea salt or eliminate salt entirely, and stop eating fish, they quietly remove their main iodine sources.

I learned this the hard way early in my career. I was counseling patients to reduce sodium, and they were cutting out iodized salt without replacing the iodine. Their TSH (thyroid stimulating hormone) started creeping up. Once we identified the iodine deficiency and replaced it, their thyroid function normalized.

T3 (your active thyroid hormone) is literally three iodine molecules. T4 is four. You need iodine to make thyroid hormone. If it is too low, hypothyroidism follows. But too much can also cause thyroid problems, which is why I have seen patients walk in on 1,000 micrograms of supplemental iodine and run into trouble.

You need around 150 micrograms per day, roughly a quarter to half teaspoon of iodized salt. Seaweed and nori are good sources. The gold standard test is a 24-hour urine iodine collection, which yes, means collecting your urine for an entire day and keeping it in the fridge. A serum level is less reliable unless you are significantly depleted.

One more thing: the worry about soy and cruciferous vegetables damaging your thyroid is only relevant if your iodine is low. I have Hashimoto’s thyroiditis. I have been eating soy, broccoli, kale, and cauliflower for 14 years on a whole food plant-based diet, and my thyroid medication dose actually decreased when I went plant-based because the inflammation in my body went down. So eat those foods. Just make sure your iodine is sufficient.

Potassium

Potassium-rich foods help buffer sodium intake and support healthy blood pressure. Symptoms of low potassium include muscle cramps, fatigue, palpitations, and elevated blood pressure. It shows up reliably on a basic or comprehensive metabolic panel, which your doctor is likely already checking.

Most adults probably get about half of what they need. Potatoes, bananas, avocados, and dark leafy greens are all excellent sources. If you are on a diuretic, pay extra attention. People with kidney disease (stage 3 and beyond) need to work with their nephrologist to monitor potassium closely.

I want to share a story from a patient in Canada. She had reversed her type 2 diabetes on a whole food plant-based diet, lost close to 100 pounds, and come off her blood pressure medications. Then her doctor told her that her elevated potassium was caused by her plant-based diet. Her kidney function was perfect. I told her this was almost certainly a lab artifact. When blood sits too long before being processed, or when the blood draw is traumatic (the needle jostles, cells rupture, potassium spills out), you get a falsely elevated reading. We had her redraw from both arms, well-hydrated, no fist clenching, and her potassium came back completely normal. Lab error is the number one cause of falsely elevated potassium when kidney function is intact. Stay hydrated before your draw and do not let one result panic you.

B Vitamins (Beyond B12)

Dr. Miller took us through the broader B vitamin family. These are found in leafy greens, nuts, seeds, legumes, whole grains, lentils, and avocados. When levels are low, you might notice decreased energy, altered mood, brain fog, or poor sleep.

An important piece of this puzzle is methylation. Some B vitamins need to be methylated (activated) before your body can use them, and genetic variations in the MTHFR pathway can impair that process. Dr. Miller shared a case of a patient eating a comprehensive diet with plenty of plants who could not sleep and had persistent low energy. Genetic testing revealed a methylation issue. Targeted supplementation with B2, B3, B6, and B9 (folate) significantly improved her sleep, mood, and focus.

A few warnings here. Taking high doses of B vitamins without a clear reason can backfire. Certain people cannot metabolize large amounts and will feel worse, not better. B6 toxicity specifically can cause nerve tingling and numbness. And if you get cracking at the corners of your mouth, unexplained rashes, or slow wound healing, consider whether B vitamin status might be a factor.

Choline

This is one I do not think gets enough attention. When I audit my own diet on Cronometer, I was hitting my targets for calcium, iron, and everything else, but I was only getting about half the choline I needed as a pre-menopausal woman. After menopause, the situation gets more complicated because estrogen supports some internal choline production, and when that drops, dietary needs increase.

Low choline can contribute to fatty liver. I have had two patients with unexplained fatty liver, one in her early 40s and one in her early 50s, who had been through GI workups and liver biopsies with no answers. When we started replacing choline with phosphatidylcholine, their liver markers improved.

The richest dietary source is eggs. On a plant-based diet, soy products and cruciferous vegetables are your best options, which is another reason to not cut those food groups based on internet fear-mongering. If you have genetics that impair choline absorption, or if your diet has become too restrictive, supplementation may be warranted.

Fiber

The United States is a fiber-deficient country. The FDA recommends 25 grams per day for women and 35 grams for men, though ancestral populations likely consumed 50 to 100 grams daily. Most Americans fall well short.

Research shows that eating more than 30 different types of plants per week supports a diverse microbiome. Fiber only comes from plants, specifically fruits, vegetables, whole grains, nuts, seeds, and legumes. It is absent from animal products entirely.

If you are not used to eating much fiber and you suddenly increase your intake dramatically, your microbiome will protest. The bacteria that break down fiber need to be cultivated gradually. Start slow, increase steadily, and if you are struggling with tolerance, try blending or cooking high-fiber foods to pre-digest them somewhat. Start with lentils if beans give you trouble. They tend to be easier to tolerate.

I get 75 to 80 grams of fiber daily without trying at this point. But I grew up eating beans, vegetables, and potatoes because they were cheap, so my gut was accustomed to it long before I went fully plant-based.

Sodium

Most Americans consume too much sodium from processed foods and restaurant meals. But there is another side. People on very clean diets, particularly those who eliminate salt entirely, can develop dangerously low sodium levels.

Dr. Miller shared her own experience with hyponatremia (low sodium). She was not eating salt because she thought she was not supposed to, and it got her into real trouble. We both see this pattern: health-conscious people drinking large amounts of water, avoiding salt completely, and ending up with sodium levels around 125 (normal is 135 to 145), which is clinically significant.

Sodium is essential for nerve conduction. Every nerve signal in your body depends on sodium transport. The sweet spot for daily intake appears to be around 1,500 to 2,300 milligrams. Both too low and too high are problematic, and the relationship follows a U-shaped curve.

If your sodium runs low, step one is to check whether you are drinking too much water and eating too little salt. A pinch of iodized salt added to whole food cooking is a long way from the excessive sodium in processed food. If the simple fixes do not resolve it, a workup for kidney issues, adrenal dysfunction, SIADH, heart failure, or medication effects is appropriate.

And for the record, if anyone on the internet tells you to drink massive amounts of salt water, do not.

Protein

You can absolutely get sufficient protein on a plant-based diet. I want that to be clear. Beans, legumes, soy, whole grains, nuts, and seeds all contribute. But I do see trouble when people become overly restrictive, skip protein-rich foods because of bloating fears, or eat only fruit for entire meals.

A rough starting point for protein needs: estimate your ideal body weight (start with 100 pounds at 5 feet tall, add 5 pounds per inch, then divide by 2.2 to get kilograms). Aim for at least 1 gram of protein per kilogram, preferably 1.2, and up to 1.6 grams for people doing regular exercise. Less than 1 gram per kilogram is where I start seeing problems, especially in older adults who are already losing muscle mass.

On labs, a low creatinine can sometimes signal inadequate protein intake. And if you feel fatigued, struggle with satiety, or are not building muscle despite resistance training, protein is worth auditing. I ask patients to walk me through breakfast, lunch, and dinner. If there is no protein source at two of those meals, we have found a gap.

One of my favorite tricks: lupini bean flakes. The brand Aviate (A-V-I-A-T-E) on Amazon is excellent. A quarter cup gives you 12 grams of protein for only 80 calories. I add them to oatmeal, smoothies, soups, and chili.

Pair your protein with resistance training. You need to give your muscles a reason to hold on to the protein you are feeding them. Eating enough protein without lifting anything heavy is only half the equation.

How to Audit Your Own Nutrition

If this felt like a lot, here is where to start.

Download the app Cronometer (C-R-O-N-O-M-E-T-E-R). Log your normal eating for one week without changing anything. At the end of the week, look at where you fall short. Then decide whether you need to adjust your food choices or talk to your doctor about targeted supplementation.

For lab work, ask your physician about the following: 25-hydroxy vitamin D, serum B12 with homocysteine and methylmalonic acid, a complete metabolic panel (which includes potassium and sodium), an iron panel with ferritin, serum zinc, and an omega-3 index. For iodine, the 24-hour urine collection is the most accurate test.

Our motto for this conversation: test, do not guess. Whatever your dietary pattern, make sure it is actually working for you by checking the data. What works for one person may not work for the next. We have the same basic plumbing, but our genetics, microbiomes, absorption capacity, medications, and life circumstances make each of us a unique case.

If something does not feel right and your doctor says your labs look fine, do not stop asking questions. Sometimes the answer is in the nutrients nobody thought to check.

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