Complete digestion and absorption of ingested food calories takes approximately 30 hours from the time food is eaten.
"I mean, all the digestion takes, you know, 30 hours to complete the food digestion, right? And in the from the time you eat to the time that all the calories have been taken up, it takes probably over a day." (said at 0:46:42)
The speaker confuses total whole-gut transit time with the time required for caloric digestion and absorption. The vast majority of macronutrient digestion and caloric absorption occurs in the stomach and small intestine, taking roughly 4 to 8 hours in healthy individuals (gastric emptying typically takes 2–5 hours and small bowel transit takes 2–6 hours). The remaining time (10 to 60+ hours) occurs in the large intestine/colon, which primarily absorbs water and electrolytes and forms stool, not digesting or absorbing dietary calories.
- contradicts: How to assess regional and whole gut transit time with wireless motility capsule. (Journal of neurogastroenterology and motility 2014)
"The normal range for transit time includes the following: gastric empty-ing (2-5 hours), small bowel transit (2-6 hours), colonic transit (10-59 hours) and whole gut transit (10-73 hours)." (abstract, results, passage verified)
pubmedfull study (doi) - contradicts: Effect of bran, ispaghula, and inert plastic particles on gastric emptying and small bowel… (Gut 1997)
"Bran delayed gastric emptying by 22 (SEM 8) minutes compared with control values of 88 (SEM 6) minutes p < 0.05. Ispaghula and plastic particles had no significant effect. Small bowel transit was accelerated compared with control values of 322 (SEM 29) minutes, decreasing by 95 (29) minutes and 62 (22) minutes after bran and plastic particles respectively." (abstract, results, passage verified)
pubmedfull study (doi)