Verdict: False. The FDA says microwave ovens don't cook food from the inside out; in thick foods, the inside is cooked mainly by heat conducted from the hot outer layers.
Where the idea comes from
Microwaved food sometimes surprises people. A jelly doughnut's filling burns your mouth while the dough feels warm, or a potato's center seems hotter than its skin. Those moments make "inside out" sound right. The fact that a microwave heats without a hot element or flame adds to the sense that it works from the middle.
What the evidence says
The FDA's page on microwave ovens explains the basic mechanism: microwaves cause water molecules in food to vibrate, producing heat that cooks the food. It states that microwave ovens do not cook food from the "inside out," and that when thick foods are cooked, the inside is cooked mainly by the conduction of heat from the hot outer layers.
The jelly doughnut effect has a simpler explanation. Whirlpool's guidance on microwave cooking times notes that foods high in fat and sugar heat faster, so a sweet filling can scald while the dough around it is only warm.
Clemson Cooperative Extension's microwave food safety fact sheet explains why this matters for safety. Microwaves can heat food unevenly, and "uneven heating can create 'cold spots' where harmful bacteria may survive." Its advice is to stir or rotate food midway, let it stand for several minutes so heat spreads, and check the temperature with a food thermometer in several places. Its safe-temperature table lists 165°F for leftovers, casseroles and poultry.
What to do instead
- Spread food in an even layer, with thicker pieces toward the outside of the dish.
- Cover the dish loosely to hold in steam.
- Stir or turn the food halfway through.
- Let it stand for a few minutes before eating; the center keeps heating.
- Check leftovers with a food thermometer in more than one spot for 165°F.
Exceptions worth knowing
- •Turntables help but don't solve it. A turning tray evens out hot spots in the oven, but thick food still heats from the outside in.
- •Lower power levels give heat more time to move inward, which is why many manuals suggest medium power for large items.
- •Thawing has its own rule. Cook microwave-thawed meat right away. See whether microwave thawing makes meat unsafe.
- •Cold spots every time, even with stirring, can mean the turntable isn't turning or the microwave isn't heating at full strength.
Sources
- •FDA: Microwave Ovens (not inside out; conduction from outer layers; water molecules)
- •Clemson Cooperative Extension: Microwave Food Safety (cold spots; stir, stand, check with a thermometer; 165°F)
- •Whirlpool: Microwave Cooking Times are Too Long, Countertop Microwave (fat and sugar heat faster)
The short version: Microwaves heat the outer layer first, so stir, wait and check the center.
Cold centers even after stirring and standing can mean the turntable or the heating itself needs a look. TrueFix Los Angeles works in Glendale and nearby cities; call (213) 787-3989.