How fiber, food choices, and health changes affect your vitamin B1.
Last week, in the first part of my series, The Nutritional Blind Spot, I talked about how cancer treatment can deplete the body’s nutrients. This week, I’m turning to one nutrient that rarely gets mentioned, even though it touches nearly every part of how we feel: thiamin, or vitamin B1.
Thiamin helps your body turn food into energy and supports your nerves, brain, and heart. Your body stores only a small amount, so it depends on a steady supply from what you eat.
Most Americans have chronic nutrient deficiency. Since the Industrial Revolution, American soil, where our food is grown, has gradually been stripped of nutrients as farming has pushed it to produce faster, often with more and more pesticides. That means even a healthy diet may offer less than it once did, which makes the foods we choose matter even more.
One choice that affects B1 is often overlooked: eating fibrous foods. According to the NIH, only about 1 in 20 Americans eat enough fiber.
Fiber directly affects the way we absorb nutrients and process waste. When your diet is consistently low in fiber, your bowel movements may swing from constipated to runny. This is not normal, even if it’s normal for you.
Many fiber-containing foods naturally provide thiamin. When Americans eat fewer of these foods, they may consume less B1. Examples include:
Legumes: lentils, black beans, and peas
Seeds: sunflower seeds and flaxseeds
Nuts: macadamias and pistachios
Whole grains: oats, brown rice, and wheat germ
Vegetables: green peas and asparagus
How Modern Eating Patterns Contribute to Deficiency
Along with the foods above, pork is one of the richest sources of thiamin. When someone eats mostly processed food, their diet supplies synthetic or fortified thiamin. These added-back vitamins are not the same as naturally occurring thiamin.
Refined and fortified foods are not the same as whole-food nutrition. Milling removes much of the naturally occurring thiamin in grains, and fortification replaces selected nutrients rather than restoring the grain to its original nutritional structure. Although the added thiamin can be absorbed, a fortified cereal is not nutritionally equivalent to a minimally processed whole food.
Low-variety diets: A diet that regularly lacks legumes, nuts, seeds, whole grains, pork, or fortified grain products may provide less thiamin.
Excessive dietary restriction: Very low-calorie diets, poor appetite, restrictive eating, and meal skipping can reduce total vitamin intake. Anyone taking a GLP-1 medication should be particularly mindful of this as well.
Food preparation: Thiamin is sensitive to heat and dissolves in water, so some can be lost during cooking, particularly when cooking water is discarded.
When Illness Changes Nutritional Needs
Even a reasonably nutritious diet may not be enough when a person is experiencing circumstances that interfere with nutrient intake, absorption, or retention. Risk factors include:
Persistent vomiting or prolonged diarrhea, which can reduce intake and contribute to nutrient losses
Celiac disease and other malabsorption conditions, which may interfere with nutrient absorption
Bariatric surgery, which can alter intake and absorption and increase deficiency risk
Chronic illness or serious infection, especially when accompanied by poor appetite, increased metabolic demands, or prolonged hospitalization
Cancer treatment, which may affect appetite, gastrointestinal function, and nutrient intake
Diabetes and certain kidney conditions, which can be associated with altered thiamin status or increased losses
Thiamin is water-soluble, and the body stores only a limited amount. Under significant nutritional stress, reserves can become depleted relatively quickly. This is one reason clinicians pay particular attention to thiamin in people who have been eating very little or vomiting for an extended period.
The Bottom Line
Nutrient status depends on more than what’s on your plate. Food intake, digestion, absorption, medication exposure, illness, and nutritional demands all matter.
In the United States, nutrient deficiencies can be overlooked when healthcare focuses primarily on diagnosing and treating disease. Clinicians may not routinely assess every micronutrient, and identifying a deficiency is only the first step. Appropriate interpretation, correction, and follow-up are also important.
Looking at the Full Picture
If you’re dealing with ongoing fatigue, digestive changes, or just not feeling like yourself, it may be worth looking beyond what you eat. How well your body absorbs, uses, and holds on to nutrients matters just as much. I help clients look at the full picture, from their diet to their health history, and build a nutrition plan around what their body actually needs. And when a symptom deserves medical attention, I’ll tell you that, too.
I offer a free 15-minute discovery call. Let’s talk about what you’re experiencing and whether I can help.
