Food processing & nutrient absorption

[PsychedelicEagle]

Here's an interesting conversation I had with Claude today:

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Do whole vs. processed foods actually deliver different calories and nutrients? A look at the science.

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I had a deep dive on this and wanted to share what I learned.

The short answer: Yes, mechanical disruption of plant cell walls (grinding, chopping, milling) meaningfully changes how many calories and nutrients your body actually absorbs. The food label often lies — especially for whole nuts.

The Atwater system (why labels are imprecise)

Calorie counts on food labels are calculated using Atwater factors from the late 1800s: 4 kcal/g for protein and carbs, 9 kcal/g for fat. The label is essentially (g carb × 4) + (g protein × 4) + (g fat × 9). This assumes near-complete digestion and ignores the food matrix — i.e., the physical structure of the food.

The nut studies (USDA Beltsville group, Baer & Novotny et al.)

Using human metabolic ward studies with full fecal/urine collection and bomb calorimetry, they measured the true metabolizable energy (ME) of nuts:

• Whole almonds: ~32% fewer calories absorbed than the label says (129 kcal vs. 168–170 kcal per oz)
• Walnuts: ~21% fewer (146 kcal vs. 185 kcal per oz)
• Pistachios: ~5% fewer
• Cashews: ~16% fewer

Mechanism: Intact plant cell walls trap intracellular lipid. Chewing only ruptures so many cells; the rest passes to the colon, where some gets fermented by gut bacteria into short-chain fatty acids (butyrate, etc.) and the rest is excreted.

Processing effect on almonds (Gebauer et al. 2016, Food & Function)

Same 42g almond serving, four forms, real participants chewing normally:

• Form / Measured kcal/g (vs. Atwater)
• Whole raw / 4.42 (−30%)
• Whole roasted / 4.86 (−25%)
• Chopped / 5.04 (−22%)
• Almond butter / 6.53 (matches label)

Even just roasting (without grinding) softens the nut from 345 N to 298 N fracture force, so chewing produces smaller particles and releases ~6% more energy. Grinding to butter eliminates the matrix barrier almost entirely.

A separate study (Cassady et al. 2009) showed that chewing 40 times vs. 10 times also significantly changes lipid absorption, postprandial blood lipids, and satiety hormones. So how you chew matters too.

Micronutrient bioavailability — more nuanced

Direction depends on the nutrient:

Disruption helps: Carotenoids, lycopene, lutein. Cooking + breaking cell walls liberates them. Tomato paste > raw tomato for lycopene absorption.

Disruption hurts: Vitamin C (oxygen exposure), thiamin, niacin (heat/dehydration losses).

Plant matrix inhibits some minerals regardless: Phytic acid (in seeds, nuts, grains, legumes) and oxalic acid bind iron, zinc, calcium. Soaking, sprouting, fermentation, and leavening degrade phytate and improve mineral absorption — different axis from mechanical disruption.

So no single rule like "whole = better absorption" holds. It's nutrient-specific.

Is there an official table of "true" ME values?

Not really. USDA FoodData Central exposes two energy fields per food (Atwater general factors, and food-class-specific Atwater factors from Handbook 74), but both are calculated, not empirically measured by fecal balance. The Beltsville-style measured values exist only for a handful of nuts so far. Most other foods (legumes, grains, vegetables) haven't been measured this way at population scale.

Takeaways

The "calories" on a label is a calculation, not a measurement, and it can be off by 20–30% for whole, intact plant foods.

The "missing" calories from whole nuts aren't really lost — they feed colonic bacteria and produce SCFAs like butyrate, which has its own metabolic and gut-health benefits.

For micronutrients, processing cuts both ways depending on the nutrient. Cooking helps carotenoids; raw preserves vitamin C; soaking/fermenting helps minerals.

This is an under-studied area outside of nuts. Most foods you eat have never had their actual ME measured in humans.

Key references for anyone going deeper:

1. Novotny, Gebauer & Baer (2012) AJCN — almonds
2. Baer, Gebauer & Novotny (2016) J Nutr — walnuts
3. Gebauer, Novotny, Bornhorst & Baer (2016) Food & Function — almond processing effects
4. Cassady et al. (2009) AJCN — mastication of almonds
5. Baer, Gebauer & Novotny — pistachios, cashews
6. Grundy et al. (2015) AJCN — almond mastication and lipid bioaccessibility

 

Edited yesterday at 05:34 PM by PsychedelicEagle

[Natasha Tori Maru]

I think this has been known for a while - in fact - I recall FDA allowing manufacturers of foods containing nuts to lower their macronutrient breakdowns on labels. 

This is slightly odd, as many foods containing nuts are not whole nuts. I do not recall if they did this for nut butters.

Back when I was bodybuilding, I recall counting calories in whole nuts and I continually ended up leaner than what my calculations would output. I have since abandoned counting calories and just eat a whole foods plant based diet. I have, ever since, always eaten more nuts and never had an issue with weight gain. I even eat (gasp!) many brazil nuts - despite the claim the selenium leads to toxicity. My bloodwork is normal, and I eat 4/5 brazil nuts a day as an afternoon snack (along with walnuts). I have eaten like this for over 10 years.

Thanks for the post!

[PsychedelicEagle]

7 hours ago, Natasha Tori Maru said:

Back when I was bodybuilding, I recall counting calories in whole nuts and I continually ended up leaner than what my calculations would output.

Interesting.

7 hours ago, Natasha Tori Maru said:

I even eat (gasp!) many brazil nuts - despite the claim the selenium leads to toxicity. My bloodwork is normal, and I eat 4/5 brazil nuts a day as an afternoon snack (along with walnuts). I have eaten like this for over 10 years.

Do you do liver enzymes in your bloodwork? I was supplementing with 200ug SeMet (Selenium L-Methionine, the organic form most found in whole food) and my whole-blood selenium levels really rose, and together with it ALT & AST, which could be a downstream effect from mild Selenium toxicity.

I then stopped supplementing and stopped eating Brazil nuts for a while until the levels normalized. I'm now back to my Brazil nuts (as a good Brazilian that I am  )

One caveat with Brazil nuts is they have very large variability. From my Obsidian notes:

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The upper limit is 255-400 ug/day (updated recently to 255ug due to toxicity).
Long-term doses of 200ug have shown to not be great (TODO: see [2])

From Brazil nuts:

There is great variability of selenium content within Brazil nuts (both within and across batches)

From 1-25 ug per Brazil nut (one study);

From 8-200 ug per Brazil nut (another study);