Cold Rice Does Not Have Half The Calories
Cooling rice in the fridge changes its starch. It does not halve the calories, and the gap between those two sentences is where a lot of nonsense lives.
Here is the real effect. Gelatinized starch recrystallizes as it cools — retrogradation — and amylose and long amylopectin branches re-form double helices that digestive enzymes cannot cleave. That fraction passes to the colon instead of being absorbed.
In a 2015 crossover trial, resistant starch in cooked white rice went from 0.64 g per 100 g fresh, to 1.30 g after ten hours at room temperature, to 1.65 g after 24 hours at 4°C and reheating. Glycemic response in fifteen healthy adults dropped from 152 to 125 mmol·min/L. That is a real, measured, statistically significant difference.
It is also 1.65 grams per hundred. Roughly one and a half percent of the food. Refrigerating your rice is not a calorie-deletion technique, and anyone selling it as one is counting on you not reading the number.
The caveats are honest ones: fifteen people, one country, one rice, single-blind. The authors themselves note an earlier Indonesian study found no effect when reheating followed cooling, and attribute the discrepancy to reheating reversing part of it. Retrograded amylopectin becomes digestible again at only 40–60°C.
The genuinely useful part is a coincidence. The food-safety advice for leftover rice and the resistant-starch advice are the same advice: cool it fast and refrigerate it. One of those reasons is worth caring about. We will let you guess which.