fiber = carb or fat or nothing?

[Todd Allen]

In CRONOMETER fiber grams appear under carbohydrates and the full weight of them is applied to calories as if they are carbs.  But from what I've read we hardly digest insoluble fiber at all.  Soluble fiber is more readily digested through a process of fermentation in the gut but the end result appears to be somewhat mixed with at least some of it being converted to short chain fatty acids which get absorbed by the body as fat.  Also, it appears fiber can inhibit digestion of some otherwise readily digestible carbs.

 

CRONOMETER doesn't break out the type of fiber so even if one knew a more appropriate way to apply the grams of fiber as calories of the various macro nutrients it doesn't seem possible.   Does anyone know of better tools or resources to track calories and in particular is more accurate at quantifying the calories the body sees as carbs and fats?

[Michael R]

All:
 

In CRONOMETER fiber grams appear under carbohydrates and the full weight of them is applied to calories as if they are carbs. 

 

Nope. COM uses "modified Atwater." Still far from perfect in practice — see eg. the effect of amount of chewing on nuts, and the different magnitude of the effect between almonds (2,3) and pistachios (4) in the same lab — but they definitely do account for differences in biological assimilation, albeit itself imperfectly.
 

But from what I've read we hardly digest insoluble fiber at all.  Soluble fiber is more readily digested through a process of fermentation in the gut but the end result appears to be somewhat mixed with at least some of it being converted to short chain fatty acids which get absorbed by the body as fat. 

 

The additional snag is that it's not quite clear how much of those SCFA get absorbed, and likely varies by the region in the gut in which they're produced and a person's background microbiome when they eat the food: in some areas, they'll be taken up by other symbiotic organisms if they're available, and in others they get absorbed by you or pass through you intact.

 

I don't believe anyone can do better than COM on this: that's just the state of the science.

 

References

[1] http://www.ncbi.nlm.nih.gov/pubmed/22760558Am J Clin Nutr. 2012 Aug;96(2):296-301. doi: 10.3945/ajcn.112.035782. Epub 2012 Jul 3. Discrepancy between the Atwater factor predicted and empirically measured energy values of almonds in human diets. Novotny JA, Gebauer SK, Baer DJ. PMCID: PMC3396444 PMID: 22760558 [PubMed - indexed for MEDLINE]

2. Am J Clin Nutr. 2009 Mar;89(3):794-800. Epub 2009 Jan 14. Mastication of almonds: effects of lipid bioaccessibility, appetite, and hormone response. Cassady BA, Hollis JH, Fulford AD, Considine RV, Mattes RD. PMID: 19144727 http://www.ajcn.org/content/89/3/794.long

3. Effects of appetite, BMI, food form and flavor on mastication: almonds as a test food J M Frecka, J H Hollis and R D Mattes Eur J Clin Nutr 62: 1231-1238 pubmed/17637602 http://ucce.ucdavis.edu/files/datastore/608-21.pdf

4. Baer DJ, Gebauer SK, Novotny JA. Measured energy value of pistachios in the human diet. Br J Nutr. 2012 Jan;107(1):120-5. doi: 10.1017/S0007114511002649. Epub 2011 Jun 28. PubMed PMID: 21733319.

 

[Todd Allen]

As an example in CRONOMETER

1 tbsp chia seed

carbs 4.2 grams

fiber 3.4 grams

starch 1.0 grams

sugar 0.2 grams

carbohydrate 17.2 kcal

 

17.2 / 4.2 = 4.095

I don't know what the Atwater conversion factor is for chia seed, but given that > 80% of the carbs are fiber it seems unlikely that 4.095 is correct