Coffee, Tea: False Allies?

Coffee, Tea, and Anti-Nutrients
Should we worry about invisible interactions with our nutrients and medications?
by Laurent Glatz – for Athletic Carnivore

An Ordinary Drink, Uncommon Effects

In popular imagination, coffee is an ally. It wakes us up, stimulates, and accompanies morning conversations. Tea, on the other hand, embodies moderation and longevity. Yet, some clinicians, including Dr. Anthony Chaffee, an Australian surgeon and advocate of a strict carnivore diet, put forward a radical critique: coffee and tea contain anti-nutrients capable of hindering the absorption of vitamins, minerals, proteins, fats, and even medications.

This claim deserves scrutiny. Behind the controversy lie real biological mechanisms.

Coffee and tea are plant extracts rich in bioactive compounds. Among them are tannins, polyphenols, certain saponins, and in other plant matrices, phytic acid. All belong to the category of “anti-nutrients,” a term describing substances that can bind to nutrients and reduce their intestinal absorption.

Tannins, abundant in black tea and present in coffee, have a particular affinity for non-heme iron. They form insoluble complexes with it in the small intestine, decreasing its bioavailability. This phenomenon has been documented for several decades: consuming tea or coffee at mealtime can significantly reduce the absorption of plant-based iron.

In an omnivorous individual consuming heme iron from animal sources, the impact is lessened. But in subjects already presenting low ferritin or iron-deficiency anemia, co-ingestion of tannin-rich beverages can worsen the situation.

Polyphenols can also interact with certain minerals like zinc or calcium, although the effect varies depending on dose, food matrix, and the individual’s nutritional status.

When Medication Absorption Comes Into Play

The issue becomes more sensitive when it concerns medications.

Levothyroxine, the standard treatment for hypothyroidism, is known to be particularly sensitive to absorption conditions. It must be taken on an empty stomach, ideally with water, and away from any food, supplement, or beverage other than water. Studies have shown that simultaneous intake of coffee can reduce levothyroxine absorption, likely due to changes in gastric pH and interactions with intestinal transporters.

Clinically, this can result in unstable TSH blood levels despite regular medication intake. Some patients then require higher doses, not because their condition worsens, but because the medication is not properly absorbed.

This phenomenon is not theoretical. It is measurable. Endocrinologists explicitly recommend waiting at least 30 to 60 minutes, sometimes longer, before consuming coffee or tea after taking levothyroxine.

Caffeine, Minerals, and Recovery

Beyond medications, caffeine itself exerts physiological effects that may influence mineral status.

Caffeine is a mild diuretic. It increases glomerular filtration and can enhance urinary excretion of calcium and, to a lesser extent, magnesium. The effect remains moderate in habitual consumers due to partial renal adaptation, but it is real.

In individuals already marginally deficient in magnesium, or athletes subjected to significant sweat losses, high caffeine consumption could contribute to maintaining a suboptimal state.

Dr. Chaffee’s concern goes further. In his practice, he observes that some patients following a strict carnivore diet do not reach optimal biological markers as long as they consume coffee. He also suggests that muscle recovery could be impaired, with some patients reporting more pain after several days of training.

Biologically, several hypotheses can be discussed.

Caffeine acts by blocking adenosine receptors, increasing neuronal excitability and catecholamine release. It stimulates the sympathetic nervous system. In the short term, this improves alertness and performance. But chronically elevated sympathetic tone could theoretically affect recovery, deep sleep quality, and hormonal regulation.

Sleep, in particular, plays a central role in muscle repair and immune regulation. Late caffeine consumption can reduce deep sleep, even if the subject does not perceive overt insomnia.

As for the impact on proteins and fats, there is no solid data showing that coffee significantly prevents their absorption in a healthy individual. The described interactions mainly concern minerals and certain medications.

It is therefore important to distinguish proven mechanisms from extrapolations.

Yes, coffee and tea contain compounds capable of reducing the absorption of certain micronutrients.
Yes, they can interfere with levothyroxine absorption and potentially other sensitive medications.
Yes, caffeine can increase urinary excretion of certain minerals.

But these effects depend on dose, timing, nutritional status, and clinical context.

The most troubling question may not be whether coffee is “good” or “bad.” It is how many patients increase their medication doses without anyone questioning their morning habits.

How many take their thyroid medication with an espresso, convinced they are following their prescription correctly?

Timing Changes Everything

The minimal precaution is to space coffee and tea at least one to two hours away from medications, mineral supplements, and iron-rich meals if one seeks to optimize absorption.

To delve deeper into analyzing your nutritional functioning, you can also [take the free questionnaire](/en/questionnaire-neuroprofil.html).

Coffee is neither a poison nor an elixir. It is a pharmacologically active substance, socially normalized.

And like any active substance, it deserves to be consumed with full awareness.