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Dean Pomerleau

USDA to Revise Official Estimate of Calories in (Wal)nuts

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Many CR practitioners, including me, consume a lot of nuts, for their benefits to health (e.g. reduced CVD) and mortality. And it is been pretty common knowledge among those who follow this stuff closely, that it is surprisingly hard to get fat eating nuts. In fact, several years ago, Dr. Greger had did a 7-part video series (beginning here) seeking to explain the missing calories in nuts by looking at all the various theories. I highly recommend watching for those who haven't.

 

Now, it finally looks like the USDA is waking up to the issue of missing calories in nuts, specifically walnuts. In this new study [1], discussed here, researchers at the FDA tracked 18 people in very controlled conditions on a diet lacking or supplemented with walnuts. They took samples of what they ate, and what they excreted, and determined that walnuts, "consistent with other tree nuts", contained 21% fewer available calories than predicted by the Atwater method typically used to compute calorie content of foods, basically a sophisticated version of the 9-4-4 Fat-Carb-Protein method for estimating calories. 

 

They found walnuts contained 5.22 kcal/g, rather than 6.61 kcal/g as predicted by Atwater. They said their finding could result in changes to food labelling practices. And as the authors indicate, this lower calorie content than predicted is almost certainly true of other nuts as well. No word on seeds though...

 

As of now, the USDA food database, and hence CRON-O-Meter and other diet tracking tools, still used 6.61 kcal/g (actually I just checked, CRON-O-Meter uses 6.54 kcal/g) rather than the lower, more realistic, 5.22 kcal/g. 

 

--Dean

 

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[1] J Nutr. 2015 Nov 18. pii: jn217372. [Epub ahead of print]

Walnuts Consumed by Healthy Adults Provide Less Available Energy than Predicted
by the Atwater Factors.

Baer DJ(1), Gebauer SK(2), Novotny JA(2).

Author information:
(1)USDA, Agricultural Research Service, Beltsville Human Nutrition Research
Center, Beltsville, MD David.Baer@ars.usda.gov. (2)USDA, Agricultural Research
Service, Beltsville Human Nutrition Research Center, Beltsville, MD.

BACKGROUND: Previous studies have shown that the metabolizable energy (ME)
content (energy available to the body) of certain nuts is less than predicted by
the Atwater factors. However, very few nuts have been investigated to date, and
no information is available regarding the ME of walnuts.
OBJECTIVE: A study was conducted to determine the ME of walnuts when consumed as
part of a typical American diet.
METHODS: Healthy adults (n = 18; mean age = 53.1 y; body mass index = 28.8
kg/m(2)) participated in a randomized crossover study with 2 treatment periods (3
wk each). The study was a fully controlled dietary feeding intervention in which
the same base diet was consumed during each treatment period; the base diet was
unsupplemented during one feeding period and supplemented with 42 g walnuts/d
during the other feeding period. Base diet foods were reduced in equal
proportions during the walnut period to achieve isocaloric food intake during the
2 periods. After a 9 d diet acclimation period, subjects collected all urine and
feces for ∼1 wk (as marked by a Brilliant Blue fecal collection marker) for
analysis of energy content. Administered diets, walnuts, and fecal and urine
samples were subjected to bomb calorimetry, and the resulting data were used to
calculate the ME of the walnuts.
RESULTS: One 28-g serving of walnuts contained 146 kcal (5.22 kcal/g), 39
kcal/serving less than the calculated value of 185 kcal/serving (6.61 kcal/g).
The ME of the walnuts was 21% less than that predicted by the Atwater factors (P
< 0.0001).
CONCLUSION: Consistent with other tree nuts, Atwater factors overestimate the
metabolizable energy value of walnuts. These results could help explain the
observations that consumers of nuts do not gain excessive weight and could
improve the accuracy of food labeling. This trial was registered at
clinicaltrials.gov as NCT01832909.

© 2016 American Society for Nutrition.

PMID: 26581681

 

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This opens up a proverbial can of worms.

 

My understanding is that in the case of almonds, while they appear to contain a lot of calories (a full day's supply of calories - 1800 of them - can be found in 311 g of almonds) even after being thoroughly chewed, much of the fat in them has been found to be unabsorbed.  This has certainly been my experience.  From time to time I have eaten rather large quantities of almonds and, despite their supposed substantial caloric content, it has never seemed to affect my weight.  This might sound like a good way to satisfy hunger without the consequences for body weight. 

 

However, if much of the fat calories are not being absorbed, what about the micronutrients?  While 1800 calories of almonds *contain* more than five times the RDA for vitamin E, how do we know how much, if any, of the vitamin is being absorbed?  

 

But worse, this brings into question the entire subject of assessing nutrient adequacy on the basis of intake.  We may be *swallowing* enough of each of the micronutrients, but how do we know if we are absorbing enough of them?  In the case of almonds it seems to be a generalized problem (i.e. probably everyone fails to absorb a sizeable proportion of their fat calories.)  But there are undoubtedly also differences between individuals in their ability to absorb a wide range of nutrients.

 

The solution - perhaps widely available 50 years from now - may be to assess our blood (or some other repository) levels of each nutrient.

 

We already do that for vitamin D, and for many people the results of those tests have been a revelation.  To be confident about of our 'Triage Theory of Nutrition' long term health status, we may need to find a way to do it for everything else as well.

 

Rodney.

 

============

 

"The unverified conventional wisdom is almost invariably mistaken."

Edited by nicholson

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Rodney,

 

I agree entirely. We should take the nutrients provided in foods as specified in the USDA database with a pretty big pinch of salt.

 

You talk about Vitamin E. I find iron to be a great example for me. I get many times the RDA for iron both from food and supplements, but despite this my serum iron level, hemoglobin, and iron stores (ferritin) remain at the bottom edge of the reference range (which I consider a good thing, FWIW).

 

Absorption of calories and other nutrients likely depends on a host of factors, including thoroughness of chewing, one's microbiome, interactions between foods/nutrients, fiber & transit time, cooking/processing, how the nutrient is bound in the plant matrix, anti-nutrients that inhibit absorption, etc.

 

Quite honestly, while I recommend it for beginners, I have little faith these days in using tools like CRON-O-Meter to micromanage one's diet/nutrients, except for avoiding frank deficiencies, as a result of all this uncertainty & variability.

 

--Dean

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Absorption of calories and other nutrients likely depends on a host of factors, including thoroughness of chewing, one's microbiome, interactions between foods/nutrients, fiber & transit time, cooking/processing, how the nutrient is bound in the plant matrix, anti-nutrients that inhibit absorption, etc.

 

Quite honestly, while I recommend it for beginners, I have little faith these days in using tools like CRON-O-Meter to micromanage one's diet/nutrients, except for avoiding frank deficiencies, as a result of all this uncertainty & variability.

 

--Dean

 

Dean, I'll comment on the study and mostly echo what you said.

 

It looks like the study you posted fed walnuts and checked fecal excretion and caloric balance to maintain weight to estimate an absorbable calorie load. I think the take-home idea is important, but it does make tracking calories (and micronutrients) difficult.

 

I usually chew my food very thoroughly so I may be able to access more of the nuts' calories. Same for those who add nuts to smoothies or who soak nuts to make them more easily digestible. As you said, this same phenomenon applies to the thoroughness of cooking, overall bulk consumed in the diet, etc. Taken further, I bet the margin of error for standard food amounts (1 slice of bread, 1 medium apple, etc.) or visually estimated amounts (1 cup, 1 tbsp, etc.), which many people use is a more significant concern.

 

Tracking nutrition using CRON-O-Meter or similar is just an estimate, but an informed estimate. I think the consistency is the most important variable. Does it really matter if I get 195 vs. 155 calories per ounce of walnuts, or that today's slice of bread was 40 vs. 44 grams, or is it more important that I have a consistent system with fixed values to use that I can decide to increase or decrease based on my goals? More detailed and accurate data certainly helps, but for most people I think the concept of just keeping track of what you eat and using some metric (accurate or not) for consistent comparison is the most worthwhile benefit.

 

As such, these days I'm far less bothered if I don't track something in CRON-O-Meter, if I'm even tracking at all. I eat a mostly consistent diet and have settled on a certain selection of staple foods with a given caloric density such that I can intuitively consume a comfortable amount to meet my desires and not consume excess calories. Part of me enjoys tracking and feeling 100% certain, especially when I'm stressed, sleep deprived, or otherwise bored--times when I have more difficulty restraining my intake. I've been slowly transitioning to a more intuitive dietary regiment and it seems to be mostly successful. I hated feeling the need for a scale to "safely" consume food, and I was avoiding some completely acceptable foods I enjoy only because they weren't in the database, so it was obviously time for an intervention.

 

Also, I didn't see anything in your post or with a quick Google search that suggested the USDA planned to update their calorie values in their database. Did you see this mentioned somewhere?

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Hi James,

 

I like and share your style of eating consistently and tracking other metrics. I track my weight pretty carefully to make sure my net calories over time are consistent. It appeared from the CR poll a while back that most long-term CR practitioners adopt a similar strategy of less careful tracking and instead eating a more consistent diet day-to-day

 

 

Also, I didn't see anything in your post or with a quick Google search that suggested the USDA planned to update their calorie values in their database. Did you see this mentioned somewhere?

.

You're right.. They didn't explicitly mention changing the USDA database for calories in walnuts. I took it as an implication from the fact that these were USDA researchers who did the study and presumably it's their job to see their research gets disseminated to improve the food labeling system. Plus they mentioned in the abstract that their results "could improve the accuracy of food labeling". I guess time will tell if/when their results get reflected in the USDA food database.

 

--Dean

 

 

 

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I've been meaning to comment on this post for a while now. I wanted to reconstruct a very long draft of a post I'd written right after my computer crash -- I thought I had a good temporary system in place as I was waiting for the online restore, but I lost the post.

 

In any event. I want to echo everything said here. Also, like James, I've been trying to chew very, very thoroughly. I referenced in my draft post a discussion in the archives started by Al Pater (and Dean, I think) about almond chewing and absorbed calories. The discussion was centered on this study, I think, but the archives are (as usual these days) down, so I can't be certain:

 

Effect of mastication on lipid bioaccessibility of almonds in a randomized human study and its implications for digestion kinetics, metabolizable energy, and postprandial lipemia

 

Conclusions: Following mastication, most of the almond cells remained intact with lipid encapsulated by cell walls. Thus, most of the lipid in masticated almonds is not immediately bioaccessible and remains unavailable for early stages of digestion. The lipid encapsulation mechanism provides a convincing explanation for why almonds have a low metabolizable energy content and an attenuated impact on postprandial lipemia.

 

Whoops, wait, now I found it. It was this study:

 

Mastication of almonds: effects of lipid bioaccessibility, appetite, and hormone response

 

That study actually focused on effects on satiety, but our discussion moved into the question of nutrient avail.

 

A few other studies worth looking at:

The effects of processing and mastication on almond lipid bioaccessibility using novel methods of in vitro digestion modelling and micro-structural analysis (free full text not avail.)

 

Impact of cell wall encapsulation of almonds on in vitro duodenal lipolysis

 

Discrepancy between the Atwater factor predicted and empirically measured energy values of almonds in human diets
 

Measured energy value of pistachios in the human diet (free full text not avail.)

 

The studies reveal differences with the results of the Atwater method of between 5 and nearly 20%.

 

(Note: many of these researchers think the lack of availability of lipids is a good thing.)

 

James, you mention soaking. I think soaking will increase nutrient availability, but I wonder what's lost in the soak water (which I don't want to consume because it will have a lot of antinutrients - part of the point of soaking: to remove antinutrients). There's certainly a lot of the color of the walnut pellicle that I see washed away: that means a lot of potentially beneficial phytonutrients are lost. And the content of some minerals would likely be diminished, as well, I imagine. But how much would depend on their "fixedness" in the matrix of the nut or seed.

 

In any event, I'm sure I'm not the only one who has noted that her/his poop isn't perfectly isotropic. Indeed, I've seen whole sunflower seeds. But: no longer, now that I'm REALLY making an effort to chew thoroughly. But I still suspect that a piece of nut or seed that's 1-2 mm3 instead of 10-20 mm3 as it enters the stomach is not going to have all its nutrients extracted and absorbed before exiting.

 

By the way, tips on chewing more thoroughly: take smaller bites (or toss fewer nuts in your mouth). I actually was unable to chew more thoroughly for months until I started doing this! Bizarre. I wrote reminder notes all over the place, and I'd chew thoroughly for a minute or so once I started a meal, but then would go back to my normal chewing. It just wasn't happening. It was weird, like it was an autonomic function. (Try to breath in a different way. You'll revert back to normal very quickly.) But the bite size was not like an autonomic function, so that I was able to change, and, from there, more thorough chewing became natural.

 

Zeta

Edited by Zeta

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Zeta,

 

Thanks for all the additional info on the importance of chewing nuts for thorough nutrient extraction. But why go to all that trouble when you can let technology do the job?

 

As I mentioned in my recent post about chestnuts on the "Which nuts are best" thread, I've been pulverizing my nut mixture in a food processor and my seed mixture in a coffee grinder into a pretty fine, only slightly granular, consistency before eating them. I grind a weeks worth this way and store it in the fridge.

 

By grinding nuts/seeds this way I maximize their surface area and therefore digestibility without the need for a tremendous amount of chewing, and without the loss of nutrients associated with soaking.

 

Since I've been doing this practice, I no longer see chunks of nuts or seeds in my stool.

 

--Dean

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Well, now that I'm used to thorough chewing, I don't mind it. And I'm going to keep soaking, for reasons I intend to address thoroughly at some point, so the question is what device will pulverize soggy nuts in a way I can deal with. I own a Krups coffee grinder, and a pretty powerful blender. Both do indeed pulverize the soaked nuts, but the clean up (and, simply: the transfer of nuts to my mouth) takes so much time it's not worth it: I end up having to work to get the last bits. (Not so with non-soaked things, though, like flax seeds.)

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Zeta,

 

And I'm going to keep soaking, for reasons I intend to address thoroughly at some point,

 

Soaking makes sense for someone such as yourself with digestion problems. But I don't place much stock in the Weston Price Foundation for nutritional advice :)xyz - e.g. their promotion of bacon as a health good. The WPF link you post discusses the downside of phytic acid in nuts, and why its good to soak them to get rid of it.

 

It appears to me (as discussed here) that there are substantial benefits to phytic acid, as well as downsides - in particularly reduced iron and zinc absorption. That's why I take iron and zinc supplements away from meals.  Note - in all the epidemiological studies and clinical trials showing tremendous benefits of nut consumption (including this brand meta-analysis [1] posted by Al which found a 20% lower risk of all-cause mortality in the highest (vs. lowest) quintile of half a million nut consumers), none (or virtually none) of the participants in these studies were consuming soaked nuts. This isn't to say soaking necessarily reduces nutrition or benefits of nuts, but the existing evidence is for non-soaked nuts.

 

I own a Krups coffee grinder, and a pretty powerful blender. Both do indeed pulverize the soaked nuts, but the clean up (and, simply: the transfer of nuts to my mouth) takes so much time it's not worth it: I end up having to work to get the last bits. (Not so with non-soaked things, though, like flax seeds.)

 

A (typical) coffee grinder is far to small for me to efficiently chop nuts with, particularly since in order to save time I chop an entire week's worth at once, which I store in the freezer.

 

Ironically, today the trusty food processor I've had for many years (a GE Variable speed 9-cup model #106622) gave up the ghost while chopping nuts. So I had to fall back to using my Vitamix blender. Boy you are right - what a pain!

 

The Vitamix (at least with the standard 64oz carafe) does a much poorer job of chopping nuts uniformly than my food process - some of it turns almost into nut butter (i.e. becomes a sticky paste), while some of the nuts are still nearly whole, even with rapid agitation with the pulse and tamper to try to stir them up. Plus you are totally correct that its a real pain to get the chopped nuts out of the Vitamix carafe - particularly since some of the nuts gets turned into a fairly sticky nut paste that clings to the bottom of the carafe, beneath the blades.

 

highly recommend to you or anyone interested in chopping nuts to use a s-bladed food processor, rather than a blender or a coffee grinder. I just researched and purchased this Hamilton Beach Food Processor ($30 from Amazon with free prime shipping, also available locally at Target stores for the same price), as a replacement for my now broken GE model.

 

--Dean

 

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[1] Br J Nutr. 2016 Jan;115(2):212-25. doi: 10.1017/S0007114515004316. Epub 2015 Nov 

9.
 
A systematic review and meta-analysis of nut consumption and incident risk of CVD
and all-cause mortality.
 
Mayhew AJ(1), de Souza RJ(1), Meyre D(1), Anand SS(1), Mente A(1).
 
Author information: 
(1)1Department of Clinical Epidemiology and Biostatistics,McMaster
University,Hamilton, ON,Canada, L8N 3Z5.
 
Dietary patterns containing nuts are associated with a lower risk of CVD
mortality, and increased nut consumption has been shown to have beneficial
effects on CVD risk factors including serum lipid levels. Recent studies have
reported on the relationship between nut intake and CVD outcomes and mortality.
Our objective was to systematically review the literature and quantify
associations between nut consumption and CVD outcomes and all-cause mortality.
Five electronic databases (through July 2015), previous reviews and
bibliographies of qualifying articles were searched. In the twenty included
prospective cohort studies (n 467 389), nut consumption was significantly
associated with a lower risk of all-cause mortality (ten studies; risk ratio (RR)
0·81; 95 % CI 0·77, 0·85 for highest v. lowest quantile of intake, P het=0·04, I 
2=43 %), CVD mortality (five studies; RR 0·73; 95 % CI 0·68, 0·78; P het=0·31, I 
2=16 %), all CHD (three studies; RR 0·66; 95 % CI 0·48, 0·91; P het=0·0002, I
2=88 %) and CHD mortality (seven studies; RR 0·70; 95 % CI 0·64, 0·76; P
het=0·65, I 2=0 %), as well as a statistically non-significant reduction in the
risk of non-fatal CHD (three studies; RR 0·71; 95 % CI 0·49, 1·03; P het=0·03, I 
2=72 %) and stroke mortality (three studies; RR 0·83; 95 % CI 0·69, 1·00; P
het=0·54, I 2=0 %). No evidence of association was found for total stroke (two
studies; RR 1·05; 95 % CI 0·69, 1·61; P het=0·04, I 2=77 %). Data on total CVD
and sudden cardiac death were available from one cohort study, and they were
significantly inversely associated with nut consumption. In conclusion, we found 
that higher nut consumption is associated with a lower risk of all-cause
mortality, total CVD, CVD mortality, total CHD, CHD mortality and sudden cardiac 
death.
 
PMID: 26548503

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