How to Choose a Quality Supplement: A Dietitian’s Guide
Walk down any supplement aisle, or scroll any wellness feed, and you'll find thousands of options promising more energy, better sleep, or glowing skin. With so many choices, how do you know which products are worth your money, and which are even what they say they are? As registered dietitians, we get this question every week. Here's the checklist we use, and how you can use it too.
Start with food (and a reason)
A supplement should fill a specific gap, not replace a balanced eating pattern. Before buying anything, ask yourself: what am I hoping this will support, and is there a food-first way to get there? Many nutrients, including fiber, omega-3 fats, and most vitamins and minerals, are absorbed and used well from whole foods. A supplement makes the most sense when your intake is limited, your needs are higher, or your dietitian or healthcare provider has identified a specific reason.
Understand how supplements are regulated
In the US, dietary supplements are regulated differently from prescription drugs. The FDA does not approve supplements for safety or effectiveness before they are sold. Manufacturers are responsible for making sure their products are safe and accurately labeled, and they must follow current Good Manufacturing Practices (cGMPs). That means quality can vary widely from brand to brand, and choosing a reputable source matters.
Look for third-party testing
Independent testing is one of the best signals of quality. Third-party certification programs check that a product contains what the label says, in the amounts listed, and that it isn't contaminated with unsafe levels of things like heavy metals or microbes. Look for seals such as:
USP Verified: confirms identity, potency, purity, and manufacturing quality.
NSF/ANSI 173 (NSF Contents Certified): confirms label accuracy and checks for contaminants.
NSF Certified for Sport® or Informed Sport: an extra screen for substances banned in sport, which is useful for athletes.
No seal? Ask the company whether it can provide a Certificate of Analysis (COA) for the batch you're buying. Reputable manufacturers can.
Read the Supplement Facts label like a dietitian
Form and dose: check the form of each nutrient (for example, magnesium glycinate vs. magnesium oxide) and the amount per serving, not just per capsule.
% Daily Value: very high percentages aren't automatically better. More than you need can crowd out other nutrients or cause side effects.
Proprietary blends: blends list a total weight but not the amount of each ingredient, so it's harder to know what you're getting.
Other ingredients: scan for allergens, fillers, colors, or sweeteners you want to avoid.
Bold claims: be cautious with products that promise to "cure," "detox," or work "instantly." Those are red flags.
Check for interactions and personal fit
"Natural" doesn't always mean "safe for you." Some supplements can interact with prescription medications or affect lab results, and some aren't recommended during pregnancy or breastfeeding, before surgery, or for children. Always share your full supplement list with your dietitian and healthcare provider, especially if you take medications or have a medical condition. This is one of the most valuable things a dietitian can help you sort through.
Buy from a trusted source
Where you buy matters as much as what you buy. Counterfeit or poorly stored products can show up on large online marketplaces. Practitioner dispensaries, such as Fullscript, are designed to source products directly from manufacturers and give you access to professional-grade brands that may not be sold in stores.
5 questions to ask before you buy
Why am I taking this, and how will I know if it's helping?
Is this the right form and dose for me, and for how long should I take it?
Has this product been third-party tested, and can the company share a COA?
Could it interact with my medications, other supplements, or upcoming lab work?
Am I taking any overlapping products? For example, two products that both contain vitamin D or zinc can add up quickly.
Bring these questions to your dietitian or healthcare provider, along with photos of your labels. A quick review can save you money, simplify your routine, and help you avoid taking more than you need. We also recommend reassessing your supplements every few months, since your needs can change as your eating pattern, health, and goals change.
How RINT makes it easier
Our registered dietitians have built a set of Supplement Protocols, which are curated groups of medical-grade products with clear dosing for common wellness goals like restful sleep, a healthy stress response, and healthy aging.* You can browse them anytime, and when you order through our Fullscript dispensary, you save 10–20% and your products ship anywhere in the US.
Curious about how your body responds to specific foods? You might also be interested in our post on what a food inflammation test can (and can't) tell you, or learn more about Food Inflammation Testing.
The bottom line
A quality supplement starts with a clear reason, comes from a trusted, third-party-tested source, and fits your health history and medications. When in doubt, ask a registered dietitian. That's what we're here for.
Ready to shop with confidence? Explore our dietitian-curated Supplement Protocols and save 10–20% through our dispensary.
*These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Use under your dietitian's or healthcare provider's guidance. This article is for educational purposes and is not a substitute for individualized medical advice.
