Toxins vs. toxicology: Why dose matters

Written by Tara Haelle (opens in a new tab)

Medically reviewed by Ecler Ercole Jaqua, MD, MBA, DABOM (opens in a new tab)

It’s hard to open social media or check the news these days without seeing a scary health story or alarming meme about heavy metals in foods. The media landscape is awash in seemingly nonstop heavy metal fear-mongering.Arsenic in <a href="https://www.theguardian.com/us-news/2025/apr/05/girl-scout-cookies-heavy-metals-lawsuit" rel="noopener noreferrer" target="_blank">Girl Scout cookies</a>. Lead in <a href="https://www.consumerreports.org/lead/protein-powders-and-shakes-contain-high-levels-of-lead-a4206364640/" rel="noopener noreferrer" target="_blank">protein powders</a>. Lead and cadmium in <a href="https://www.health.com/chocolate-products-heavy-metals-8399979" rel="noopener noreferrer" target="_blank">chocolate</a>.These headlines tap into a primal fear: What if the food we're eating is poisoning us?But here's what's missing from that panic: the difference between detecting a substance and that substance being dangerous. Between "this food contains lead" and "this food will harm you" lies an entire science that most headlines miss.A toxin is any substance that can cause harm to living organisms at the right (or wrong) dose.Toxicology is the science of understanding how those substances actually affect living organisms. It's about dose (that’s what this article is about!), timing, route of exposure, and how our bodies process what we consume (we dig into that in “<a href="https://science.drinklmnt.com/did-you-know/does-body-absorb-heavy-metals-bioavailability-explained" rel="noopener noreferrer" target="_blank">Bioavailability explained: What our bodies actually absorb</a>”.) It's the difference between "this exists" and "this will hurt you."Heavy metals exist naturally in trace amounts everywhere — in soil, water, and air. That means they're in our food. Not from contamination, but from the earth itself. Humans have been consuming trace amounts of these substances for <a href="https://science.drinklmnt.com/did-you-know/brief-history-of-heavy-metals" rel="noopener noreferrer" target="_blank">thousands of years</a>.What toxicology tells us is that the mere presence of heavy metals doesn't make food unsafe. What matters is how much we consume and whether that amount actually causes harm.Understanding this distinction is what separates rational food choices from fear-based ones.<h2>The 4 Principles of Toxicology (and What They Mean For Your Food)</h2>To understand the actual risks that heavy metals do — and don’t — pose in our diets, let’s examine the four key principles of toxicology: <ul><li>The dose makes the poison. </li><li>The route of exposure matters.</li><li>Bioavailability is key.</li><li>Our bodies have top-notch detox systems.</li></ul><h3>Why dose makes the poison</h3>Perhaps no adage is more important to toxicology than “the dose makes the poison.” It traces back to the 16th century physician <a href="https://www.aaas.org/taxonomy/term/10/paracelsus-man-who-brought-chemistry-medicine" rel="noopener noreferrer" target="_blank">Paracelsus</a>, whose actual words were a bit more long-winded: “In all things there is a poison, and there is nothing without a poison. It depends only upon the dose whether a poison is poison or not.”It helps to consider some specific examples: Formaldehyde is a chemical that, in large enough doses, <a href="https://www.cancer.org/cancer/risk-prevention/chemicals/formaldehyde.html" rel="noopener noreferrer" target="_blank">can cause cancer</a>. But a typical pear, weighing around 200 g, contains <a href="https://www.cfs.gov.hk/english/whatsnew/whatsnew_fa/files/formaldehyde.pdf" rel="noopener noreferrer" target="_blank">nearly 8 mg</a> of formaldehyde, and no dietitian would tell you to swear off pears for life. Even if you did, most other <a href="https://www.cfs.gov.hk/english/whatsnew/whatsnew_fa/files/formaldehyde.pdf" rel="noopener noreferrer" target="_blank">fruits and vegetables</a> contain formaldehyde too, but the amounts are so small that they don’t qualify as a “poison” to our bodies.On the flip side, water is so essential to our health that humans can survive only about three days without it. But too much of anything can be harmful, including H2O. Drinking six liters in three hours has <a href="https://www.scientificamerican.com/article/strange-but-true-drinking-too-much-water-can-kill/" rel="noopener noreferrer" target="_blank">killed people</a> from water intoxication. The Ames Test illustrates this well. Dr. Bruce Ames <a href="https://www.sciencehistory.org/stories/distillations-pod/the-ames-test/" rel="noopener noreferrer" target="_blank">developed a test</a> so sensitive it could detect mutagenic activity — mutations that could potentially lead to cancer — in everyday substances like coffee. It was a major scientific advancement. But when the media and public saw those results, they interpreted them as "coffee causes cancer."They lacked the context to understand that the world is full of substances that can cause mutations in cells at high doses, but in the tiny amounts we actually encounter them, they can't cause harm.Ames spent much of his later career emphasizing this exact point: Detecting something potentially dangerous does not mean detecting actual danger.The bottom line: Whether a substance is dangerous does not depend only on what it is. It also depends on how much you consume.<h3>Why route of exposure matters changes its risk</h3>There are multiple ways substances can enter our bodies: ingesting them through our mouths, inhaling them through our noses, absorbing them through skin contact, or injecting them directly into our bodies. And the way our bodies interact with these substances can depend on how they enter our body. We can consume some substances in food that might be dangerous if we encountered them another way. But if we eat them, our digestive system, with its strong acids and highly efficient ability to pull nutrients from our food, can dispose of them without them causing us any harm. For example, coffee. It’s a great way to get a morning dose of caffeine, but hooking yourself up to an IV of coffee could be lethal. Route of exposure matters.And let’s recall our pear example. Pears contain formaldehyde, a <a href="https://www.cancer.org/cancer/risk-prevention/chemicals/formaldehyde.html" rel="noopener noreferrer" target="_blank">known carcinogen</a>. But not only is the amount of formaldehyde in pears too small to harm us, it’s only most dangerous when we inhale large doses of it, not consume it in food. Similarly, some<a href="https://slate.com/technology/2014/03/is-formaldehyde-dangerous-no-but-johnson-johnson-removed-it-from-baby-shampoo-anyway.html" rel="noopener noreferrer" target="_blank"> shampoos have contained formaldehyde</a> that, in rare cases, can cause irritation for people with sensitive skin, but it certainly does not increase their risk of cancer.  <h3>Why bioavailability is key</h3>Just because you consume something doesn’t mean your body absorbs it. It depends on a substance’s bioavailability, the proportion of a substance that actually enters our body’s blood circulation. Route of exposure can affect bioavailability too. Some medications, such as insulin for people with diabetes or pitocin to induce labor during pregnancy, must be given through an IV, for instance, because the body cannot access enough of the drug’s active ingredients if the person takes it orally. For any substance to affect our health — positively or negatively — the body has to be able to absorb it. Sometimes even seemingly small differences in a chemical’s make-up can affect its half-life (aka, the time it takes for half of it to leave our body). Two different kinds of mercury compounds serve as good examples of this: <ul><li>Ethylmercury, which is used to prevent bacterial and fungal contamination in some pharmaceutical products, has a half-life range of <a href="https://www.who.int/groups/global-advisory-committee-on-vaccine-safety/topics/thiomersal-and-vaccines/thiomersal-vaccines#:~:text=established%20that%20the%20half-life%20of%20ethyl%20mercury%20is%203%E2%80%937%20days" rel="noopener noreferrer" target="_blank">3-7 days</a>.</li><li>Methylmercury, the kind found in fish, especially larger <a href="https://www.fda.gov/food/environmental-contaminants-food/mercury-levels-commercial-fish-and-shellfish-1990-2012" rel="noopener noreferrer" target="_blank">predator fish like tuna and sharks</a>, has a half-life range from <a href="https://www.sciencedirect.com/science/article/pii/S0304416519300297#:~:text=Understanding%20methylmercury%20(MeHg)%20toxicity%20requires,all%20individuals%20in%20a%20population." rel="noopener noreferrer" target="_blank">50</a>-<a href="https://pmc.ncbi.nlm.nih.gov/articles/PMC4555264/#:~:text=3.2.&text=We%20report%20posterior%20estimates%20calculated,variability%20in%20t1/2." rel="noopener noreferrer" target="_blank">80</a> days.</li></ul>That means ethylmercury exits our bodies much faster — with far less time for the body to absorb any of it — than methylmercury. Bioavailability also depends on how substances we consume interact with other chemicals. One reason people need vitamin D is because the vitamin is <a href="https://pmc.ncbi.nlm.nih.gov/articles/PMC2669834/#:~:text=Optimal%20vitamin%20D%20levels%20are%20necessary%20to,absorption%20increases%20to%2030%25%20to%2040%25%20%5B1%E2%80%A2%E2%80%A2%5D." rel="noopener noreferrer" target="_blank">necessary to help the body absorb calcium</a>. Drinking gallons of milk won’t substantially improve your calcium intake if you have severe vitamin D deficiency — the calcium will just exit the body. The flipside is also true: Some substances can prevent absorption. We noted above that mercury from fish has a pretty long half-life, potentially sticking around in our bodies for months. But you can reduce how much mercury your body absorbs by<a href="https://edis.ifas.ufl.edu/publication/FS437" rel="noopener noreferrer" target="_blank"> getting enough selenium</a>, as it <a href="https://www.sciencedirect.com/science/article/pii/S0161813X20301546" rel="noopener noreferrer" target="_blank">binds to mercury</a> and creates a compound that your body filters out as waste without absorbing it. Fish is a key part of a healthy diet, offering essential nutrients like omega-3s that <a href="https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/" rel="noopener noreferrer" target="_blank">reduce inflammation</a> and support <a href="https://ods.od.nih.gov/factsheets/Omega3FattyAcids-Consumer/" rel="noopener noreferrer" target="_blank">heart and brain health</a>. Avoiding fish entirely because of mercury concerns means losing those benefits, and that’s a poor trade-off for your health. The smart approach: Eat <a href="https://www.healthline.com/health/selenium-foods#fish" rel="noopener noreferrer" target="_blank">fish with a high selenium content</a>, such as yellowfin tuna, sardines, shrimp, and salmon. <a href="https://pmc.ncbi.nlm.nih.gov/articles/PMC9785339/" rel="noopener noreferrer" target="_blank">Selenium offsets the mercury</a> these fish contain, giving you the omega-3s without the risk. Understanding the actual risks versus the proven benefits gives you the knowledge to make decisions accordingly. <h3>How your body naturally detoxes heavy metals </h3>Finally, our bodies are not defenseless. Our digestive systems are remarkably sophisticated machines, designed to pull nutrients from our diet while filtering out toxins and waste. The liver and kidneys eliminate what we don’t need — including the trace amounts of heavy metals we naturally consume every day. Read more about <a href="https://science.drinklmnt.com/did-you-know/detoxification-mechanisms-how-body-clears-heavy-metals" rel="noopener noreferrer" target="_blank">how our bodies detox heavy metals</a>.<h2>How to Make Food Decisions Without Fear</h2>If we allow fear of heavy metals and other toxins in foods to drive our dietary decisions, then we run the risk of missing out on key nutrients that support long-term metabolic health. The alternative to fear-based decision-making is looking at the bigger picture, weighing the actual risks against the proven benefits, and making a decision that maximizes our health. In doing so, we also have to accept the trade-offs. We can’t eat “perfectly,” but we can eat healthfully by making practical nutrition decisions that minimize — not eliminate — trace exposures and ensure we get the essential nutrients we need to live and perform optimally.Approaching our health decisions with pragmatism instead of perfectionism can help reduce anxiety and the cognitive drain of obsessing about every potential threat (and losing the plot along the way). Constant food fear has real costs: It <a href="https://pubmed.ncbi.nlm.nih.gov/24581288/" rel="noopener noreferrer" target="_blank">harms</a> our <a href="https://www.mdpi.com/2227-9032/12/9/925" rel="noopener noreferrer" target="_blank">mental health</a>, limits dietary variety, and can create the very <a href="https://pubmed.ncbi.nlm.nih.gov/25016349/" rel="noopener noreferrer" target="_blank">nutritional deficiencies</a> we’re trying to avoid. <h3>5 questions to ask before worrying about food headlines or claims</h3>When you come across a claim about a food containing a certain toxic compound, stop and consider several questions:  <ul><li>How much of a dose am I actually consuming? Our article “<a href="https://science.drinklmnt.com/did-you-know/how-to-read-toxicology-report-convert-parts-per-billion" rel="noopener noreferrer" target="_blank">How to read a toxicology report</a>” teaches you how to calculate this for yourself. </li><li>Has that dose been shown to cause harm by public health authorities who have evaluated the consensus of research in this area? Check the FDA (for food and drinks), EPA (for environmental contaminants), or WHO (for international standards) to find out what regulatory limits exist and whether your exposure exceeds them.</li><li>Have scientists shown that consuming this substance is actually harmful compared to inhaling or injecting it? </li><li>How much of this substance will your body actually absorb? How long is its half-life? Are there other compounds you’re eating that increase or decrease how much of it your body absorbs? </li><li>Is this a substance your body’s natural detox functions are already well-equipped to filter out? </li></ul>You may not be able to answer all of these questions, but simply asking them can help slow down the panic that might overwhelm you when you first read an alarming claim about heavy metals or other toxins in foods. <h2>The Bottom Line: Balancing Caution and Context When Making Food Choices</h2>We don’t want to downplay the fact that some foods can contain harmful chemicals that we need scientists and public health authorities to work together to identify and regulate. But we have a pretty good idea of just how small a dose of heavy metals are in our foods and how little they do — and don’t — affect overall health.It’s still important to read lists of ingredients and pay attention to nutrition labels. But it’s also important to focus on the “big rocks” that will help move the needle on your metabolic health: eating adequate protein, choosing whole foods over ultra-processed ones, staying properly hydrated, getting quality sleep, managing stress. These fundamentals matter far more than obsessing over parts-per-billion measurements of trace metals in otherwise nutritious foods.Understanding the impact of <a href="https://science.drinklmnt.com/did-you-know/toxins-vs-toxicology-why-dose-matters" rel="noopener noreferrer" target="_blank">dose</a>, route of exposure, <a href="https://science.drinklmnt.com/did-you-know/does-body-absorb-heavy-metals-bioavailability-explained" rel="noopener noreferrer" target="_blank">bioavailability</a>, and <a href="https://science.drinklmnt.com/did-you-know/detoxification-mechanisms-how-body-clears-heavy-metals" rel="noopener noreferrer" target="_blank">your body’s natural detoxification</a> of the foods you consume can help you make better sense of claims you see about heavy metals in our food. To become even more proficient at understanding just how much — or how little — of a substance you’re consuming, read “<a href="https://science.drinklmnt.com/did-you-know/how-to-read-toxicology-report-convert-parts-per-billion" rel="noopener noreferrer" target="_blank">How to read a toxicology report</a>”. You’ll learn how to put “parts per billion” toxicology results into real world application. This was the second article in our six-part "Toxicology in Context: Heavy Metals" series. Want to read the other articles? Check them out below: <ul><li><a href="https://science.drinklmnt.com/did-you-know/brief-history-of-heavy-metals" rel="noopener noreferrer" target="_blank">A brief history of heavy metals in public health</a></li><li><a href="https://science.drinklmnt.com/did-you-know/heavy-metal-regulations-proposition-65-explained" rel="noopener noreferrer" target="_blank">Understanding heavy metal regulations like Prop 65</a></li><li><a href="https://science.drinklmnt.com/did-you-know/how-to-read-toxicology-report-convert-parts-per-billion" rel="noopener noreferrer" target="_blank">How to read a toxicology report: What does parts per billion mean?</a></li><li><a href="https://science.drinklmnt.com/did-you-know/does-body-absorb-heavy-metals-bioavailability-explained" rel="noopener noreferrer" target="_blank">Does your body absorb heavy metals? Bioavailability explained</a></li><li><a href="https://science.drinklmnt.com/did-you-know/detoxification-mechanisms-how-body-clears-heavy-metals" rel="noopener noreferrer" target="_blank">Mechanisms of detoxification: How the body clears heavy metals</a></li></ul> <h2>FAQs</h2>Q: Does "dose makes the poison" apply to heavy metals in food?A: Yes. Heavy metals can be harmful in large amounts but are typically harmless at the trace levels found in food. Your body has natural systems to process and eliminate small exposures.Q: Are heavy metals in vegetables dangerous?A: Trace heavy metals in vegetables are generally not dangerous. Vegetables naturally absorb minerals from soil, including tiny amounts of metals, but the nutritional benefits far outweigh these minimal exposures.Q: Why do healthy foods contain heavy metals?A: Heavy metals exist naturally in soil and water. Plants absorb nutrients and water from these sources, picking up trace amounts of metals in the process. People have had safe exposure to these trace amounts throughout all of human history.Q: Should I avoid foods with any heavy metals?A: No. Avoiding all foods with trace heavy metals would eliminate virtually all fruits, vegetables, grains, and seafood—the foundation of healthy eating.