Timing and food pairing can significantly affect how well supplements absorb. Some work better on an empty stomach, most work better with food, and a few don't care either way.
Better on Empty Stomach
Iron - Absorbs 2-3x better on empty stomach - Take 30-60 minutes before food, or 2 hours after - Vitamin C (like orange juice) improves absorption - Coffee and tea reduce absorption by 80% - If it causes nausea, take with a small amount of food (not dairy)
Certain probiotics - Some survive stomach acid better without food - Food increases stomach acid production - Soil-based organisms (SBOs) and spore-based probiotics are acid-resistant regardless - Check your specific product's recommendation
UC-II Collagen - Different mechanism than regular collagen - Works through immune modulation, not digestion - Empty stomach recommended for this specific type
Require Food (Fat Specifically)
Fat-soluble vitamins: A, D, E, K - They literally cannot absorb without dietary fat - Even a small amount of fat helps (eggs, nuts, olive oil) - Taking these fasted wastes money
Omega-3s / Fish Oil - Fat-based, absorbs better with fat in meal - Also reduces fish burps
Curcumin - Fat improves absorption (in addition to piperine or enhanced forms)
CoQ10 - Fat-soluble, take with meals
Doesn't Matter Much
Magnesium - Absorbs fine either way. Food may reduce digestive upset.
B vitamins - Water-soluble, absorb readily. Food reduces nausea.
Zinc - Food slightly reduces absorption but also reduces nausea. Your call.
Creatine - Timing doesn't matter. Just take it daily.
Collagen peptides (regular) - Unlike UC-II, these are just protein. Food timing flexible.
The Bottom Line
When in doubt, take supplements with food. The exceptions (iron, certain probiotics) are worth remembering, but most supplements absorb adequately with meals and cause fewer side effects.