“There is also a certain amount of evidence that fibre in the diet may reduce the apparent available energy from fats and proteins. When moderate amounts of fibre are introduced into the diet as wholemeal bread, fruit, and vegetables, small reductions in the energy value of all the nutrients occur, amounting to an overall fall of 2–3% in the availability of dietary energy. Further increases in the fibre content of the diet, with fruit and vegetables at the levels consumed by vegetarians, result in an additional 2–3% reduction in available energy (5).”

5. Southgate, D.A.T. & Durnin, J.V.G.A. Brit. J. Nutr., 24: 517–535 (1970).

https://www.fao.org/docrep/003/aa040e/aa040e08.htm

They are from some nutrition textbook or another.

Can you post the studies that reference these values? This seems really interesting. Thanks!

The one question I had was about the 100-150 g/day figure. I’ve looked at the papers you listed and they don’t list a exact number, one has a table comparing the different diets and just says that fiber intake was High in Palaeolithic diets compared to other diets,

The closest thing to a number I can see is a quote

“The typical
Paleolithic diet compared with the average modern Ameri-
can diet contained 2 to 3 times more fiber,”

Cordian defines a typical modern American diet intake as being 15grams in another paper:

Origins and evolution of the Western diet: health implications for the
21st century1,2
Loren Cordain, S Boyd Eaton, Anthony Sebastian, Neil Mann, Staffan Lindeberg, Bruce A Watkins, James H O’Keefe,
and Janette Brand-Miller

“The fiber content (15.1 g/d) (23) of the typical US diet is
onsiderably lower than recommended values (25–30 g) (116).”

I would appreciate it if you could clear this up for me.

My question is this: is it not insoluble fiber (ISF) that impairs nutrient digestibility?

Following are 3 studies (1 using humans, 1 using sows, and 1 using dogs) I have found that state that it is ISF that lowers the metabolizable energy (ME) content of food, not soluble fiber (SF).

Despite the human study being the most relevant, the type of fiber seems to have consistent effects across the board. I don’t know that you have access to the full texts of these studies, as I am quoting from these texts and not the abstracts to which I linked you. For your ease of reading, I have removed the parenthetical citations to older references in the quotations.

The human study:
https://jn.nutrition.org/cgi/content/full/127/4/579
“The overall effect of increasing mixed fiber sources, particularly those that contain a substantial amount of insoluble fiber, is to decrease the digestibility of energy-yielding nutrients and to decrease the amount of ME available from the diet. ”

The sow study:
https://www.ncbi.nlm.nih.gov/pubmed/18539846
“Two possible mechanisms may explain increases in energy digestibility when SF, but not ISF, is included in the diet for sows. First, SF delays gastric emptying due to its ability to swell and form a viscous material). Delayed gastric emptying improves digestive and absorptive efficiency. Second, increased SF intake increases bacterial populations in the large intestine as evidenced by increased excretion of bacteria in feces. The large populations of intestinal microbes likely increased fermentation and utilization of SF to a greater extent than ISF. Microbial fermentation in the large intestine produces VFA* that can satisfy up to 30% of the maintenance energy requirement of the pig.

In contrast to SF, ISF decreased energy digestibility of diets. Insoluble dietary fiber decreases intestinal transit time, which limits nutrient digestion and absorption. The primary components of ISF are cellulose, hemicellulose, and lignin, which are less likely to be utilized and fermented by gastrointestinal flora compared with SF. Low digestibility caused by ISF components explains why greater intakes of ISF increase the amount of plant material excreted in the feces and increases fecal bulk.”

*I could not find what VFA stood for either in the study itself or the cross references.

The dog study:
https://www.ncbi.nlm.nih.gov/pubmed/11435517
“Among the SH-containing diets, there was a linear increase in corrected fecal output as I:S increased. Insoluble fiber is associated with increased fecal bulk. The soluble fiber is available for fermentation by hindgut microflora and does not increase fecal bulk as substantially as insoluble fiber. Therefore, the higher the I:S in the SH-containing diet, the more total feces excreted.”

I apologize in advance if I am behind in the research. I am still searching the NCBI database for more studies.

-Martin

Arthur: Certainly cooking tends to increase digestible carbohydrate and caloric absorption. There’s actually a very interesting book I just read called Catching Fire by Stephen Wrangham that deals with this. Finding exacting numbers is more difficult than you might expect.

And I believe the 100-150 g/day fiber estimates come from the text of these papers.

***
Eur J Clin Nutr. 2002 Mar;56 Suppl 1:S42-52.Click here to read Links
The paradoxical nature of hunter-gatherer diets: meat-based, yet non-atherogenic.
Cordain L, Eaton SB, Miller JB, Mann N, Hill K.

Department of Health and Exercise Science, Colorado State University, Fort Collins, Colorado, USA. cordain@cahs.colostate.edu

OBJECTIVE: Field studies of twentieth century hunter-gathers (HG) showed them to be generally free of the signs and symptoms of cardiovascular disease (CVD). Consequently, the characterization of HG diets may have important implications in designing therapeutic diets that reduce the risk for CVD in Westernized societies. Based upon limited ethnographic data (n=58 HG societies) and a single quantitative dietary study, it has been commonly inferred that gathered plant foods provided the dominant energy source in HG diets. METHOD AND RESULTS: In this review we have analyzed the 13 known quantitative dietary studies of HG and demonstrate that animal food actually provided the dominant (65%) energy source, while gathered plant foods comprised the remainder (35%). This data is consistent with a more recent, comprehensive review of the entire ethnographic data (n=229 HG societies) that showed the mean subsistence dependence upon gathered plant foods was 32%, whereas it was 68% for animal foods. Other evidence, including isotopic analyses of Paleolithic hominid collagen tissue, reductions in hominid gut size, low activity levels of certain enzymes, and optimal foraging data all point toward a long history of meat-based diets in our species. Because increasing meat consumption in Western diets is frequently associated with increased risk for CVD mortality, it is seemingly paradoxical that HG societies, who consume the majority of their energy from animal food, have been shown to be relatively free of the signs and symptoms of CVD. CONCLUSION: The high reliance upon animal-based foods would not have necessarily elicited unfavorable blood lipid profiles because of the hypolipidemic effects of high dietary protein (19-35% energy) and the relatively low level of dietary carbohydrate (22-40% energy). Although fat intake (28-58% energy) would have been similar to or higher than that found in Western diets, it is likely that important qualitative differences in fat intake, including relatively high levels of MUFA and PUFA and a lower omega-6/omega-3 fatty acid ratio, would have served to inhibit the development of CVD. Other dietary characteristics including high intakes of antioxidants, fiber, vitamins and phytochemicals along with a low salt intake may have operated synergistically with lifestyle characteristics (more exercise, less stress and no smoking) to further deter the development of CVD.

***
Mayo Clin Proc. 2004 Jan;79(1):101-8.Click here to read Links

Comment in:
Mayo Clin Proc. 2004 May;79(5):703; author reply 703-4, 707.

Cardiovascular disease resulting from a diet and lifestyle at odds with our Paleolithic genome: how to become a 21st-century hunter-gatherer.
O’Keefe JH Jr, Cordain L.

Mid America Heart Institute, Cardiovascular Consultants, Kansas City, MO 64111, USA. jhokeefe@cc-pc.com

Our genetic make-up, shaped through millions of years of evolution, determines our nutritional and activity needs. Although the human genome has remained primarily unchanged since the agricultural revolution 10,000 years ago, our diet and lifestyle have become progressively more divergent from those of our ancient ancestors. Accumulating evidence suggests that this mismatch between our modern diet and lifestyle and our Paleolithic genome is playing a substantial role in the ongoing epidemics of obesity, hypertension, diabetes, and atherosclerotic cardiovascular disease. Until 500 generations ago, all humans consumed only wild and unprocessed food foraged and hunted from their environment. These circumstances provided a diet high in lean protein, polyunsaturated fats (especially omega-3 [omega-3] fatty acids), monounsaturated fats, fiber, vitamins, minerals, antioxidants, and other beneficial phytochemicals. Historical and anthropological studies show hunter-gatherers generally to be healthy, fit, and largely free of the degenerative cardiovascular diseases common in modern societies. This review outlines the essence of our hunter-gatherer genetic legacy and suggests practical steps to re-align our modern milieu with our ancient genome in an effort to improve cardiovascular health.

***
Eur J Nutr. 2000 Apr;39(2):71-9.Click here to read Links
Dietary lean red meat and human evolution.
Mann N.

Department of Food Science, RMIT University, Melbourne, VIC, Australia. neil.mann@rmit.edu.au

Scientific evidence is accumulating that meat itself is not a risk factor for Western lifestyle diseases such as cardiovascular disease, but rather the risk stems from the excessive fat and particularly saturated fat associated with the meat of modern domesticated animals. In our own studies, we have shown evidence that diets high in lean red meat can actually lower plasma cholesterol, contribute significantly to tissue omega-3 fatty acid and provide a good source of iron, zinc and vitamin B12. A study of human and pre-human diet history shows that for a period of at least 2 million years the human ancestral line had been consuming increasing quantities of meat. During that time, evolutionary selection was in action, adapting our genetic make up and hence our physiological features to a diet high in lean meat. This meat was wild game meat, low in total and saturated fat and relatively rich in polyunsaturated fatty acids (PUFA). The evidence presented in this review looks at various lines of study which indicate the reliance on meat intake as a major energy source by pre-agricultural humans. The distinct fields briefly reviewed include: fossil isotope studies, human gut morphology, human encephalisation and energy requirements, optimal foraging theory, insulin resistance and studies on hunter-gatherer societies. In conclusion, lean meat is a healthy and beneficial component of any well-balanced diet as long as it is fat trimmed and consumed as part of a varied diet.

Am I correct to assume that in these textbooks I will be able to see clear biological mechanisms that show how fiber is protective of bowel cancer? Or will I just find flimsy hypotheses based on even flimsier epidemiological studies which have countless known and unknown variables?

T