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I am looking at:

  • 100% peanut butter (no added salt, sugar, oils or anything else)
  • 100% roasted peanuts (no added salt, sugar, oils or anything else)

When looking thought different sources, I can always notice the following:

  • Peanut butter has more protein (as % of calories) than peanuts

example sources (I've looked through a dozen more, but please check others, maybe mine are not representative?):

http://www.waitrose.com/shop/ProductView-10317-10001-5588-Waitrose+LOVE+life+roasted+peanuts

http://shop.wholeearthfoods.com/collections/award-winning-peanut-butter/products/whole-earth-100-nuts-crunchy-peanut-butte-227-g

Why is this? If no ingredients are added, how is it possible for the macronutrients to change (as % of the calories). Different levels of roasting cannot be the reason because they should not change macronutrients disproportionally.

The only explanation I can think of is if in the process of making peanut butter, some part of the peanut is removed and that part contains a low protein amount. Some sources say that when peanut butter is made, the 'bitter heart of the peanut' is removed. Could that explain it?

If anyone has some insight I would be very interested to learn.

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It might be related to the article referenced in cooking.stackexchange.com/a/500/67 ; "Wrangham and his colleagues have since shown that cooking unlaces microscopic structures that bind energy in foods, reducing the work our gut would otherwise have to do. It effectively outsources digestion to ovens and frying pans. Wrangham found that mice fed raw peanuts, for instance, lost significantly more weight than mice fed the equivalent amount of roasted peanut butter." – Joe Feb 17 at 15:52
    
@Joe: except he isn't comparing raw peanuts to roasted peanut butter; he's comparing roasted peanuts to roasted peanut butter. – Marti Feb 17 at 15:54
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@Marti : see the answer I linked to -- there's other factors besides the roasting -- eg, grinding means our bodies can more fully absorb the nutrients without needing to spend energy chewing. How much of this change is fat vs. protein, though, I have no clue. – Joe Feb 17 at 15:56
    
A cynical look at the claims on the peanut butter packaging : "No added sugar or salt - contains naturally occurring sugars", "100% peanuts". Adding peanut oil might still keep those true, although I'd then expect it to be in the ingredients list. – Joe Feb 17 at 16:00
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All the label means is that the peanut butter has had nothing added to it - it does not mean that 100% of the original peanuts have been put into the peanut butter - something must be getting extracted in the process. – HorusKol Feb 17 at 21:29
up vote 43 down vote accepted

There's definitely some rounding going on because the peanut butter has 100.1g of nutrients per 100g of product. This isn't enough to explain the discrepancy. Adding up the nutrients on the roasted peanuts gives 95.4g. I think we can assume the other 4.6% is water. So perhaps more water has been driven off the peanut butter.

What I think is more likely (though could be additional) is that there's significantly less fat in the peanut butter (48.1% vs 51.7%). While this could be down to different varieties of peanut, I suspect some fat is removed in the processing, perhaps to avoid an oil slick on the surface.

Most likely of all is just different source data. Different peanuts may have been used in the calculations -- whether that is consistent with the actual ingredients used is another matter. In fact if you look at nutrition information for raw peanuts online, you'll get a range of values. There's nothing special about peanuts, the same is true for bananas. I'm sure if you look at the scientific literature on any foodstuff, you'll find a range of values published, reflecting natural variation as well as measurement variabilility -- this will then propagate to the values published to the consumer.

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This was my first thought too. If it's 100% peanuts, then there's going to be a lot of oil otherwise, so it makes sense to remove some in this case. – Jefromi Feb 17 at 16:43
    
@Jefromi running the numbers in my head, something else has to contribute as well, as the additional protein is more than the loss of fat -- but I reckon it's a significant contribution among the others I mention. – Chris H Feb 17 at 16:56
    
This is spot on. Peanut butter is not an analogy to say ground beef which would contain everything it came from. – Escoce Feb 17 at 18:15
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I think water doesn't contribute, because the questioner is looking at the ratio of protein to calories. Adding or removing water to a bucket of peanuts doesn't change the total calorie content or the amount of protein in the bucket. So although it changes both numbers per 100g of product, it doesn't change the ratio of the two. – Steve Jessop Feb 18 at 10:49
    
@SteveJessop as a % of total calories yes. I looked at the g/100g figure as there are fewer assumptions involved in that and the problem is still apparent. It's worth noting the effect of water as the peanut butter apparently has none at all. I don't think there's any foodstuff with no water. – Chris H Feb 18 at 11:49

My guess is that the peanut butter is 100% peanuts but not 100% of the peanuts are being used in it.

That's like sea salt that is 100% from the Atlantic Ocean. It still contains a smaller amount of water (and consequently a larger amount of sodium) than the Atlantic Ocean does.

Or 100% pure orange juice which fortunately omits the orange peels.

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I'm not sure that quite works. What part of the peanut do you think was removed, analogous to the peel of the orange or the water of the Atlantic? The skin of a peanut is a tiny fraction of the whole nut, and the shell is inedible so wouldn't be included in the nutrition figures for either the nut or the butter. – David Richerby Feb 18 at 0:53
    
Part to remove: the grease that builds up on the rollers. – JDługosz Feb 18 at 21:50
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+1 for chuckle at 100% sea salt containing a smaller amount of water than the Atlantic ocean. However I think you mean smaller/larger percentage rather than amount. – Don Hatch Feb 19 at 12:05

Presuming that the nutrient labels are accurate (for some value of "accurate"), I can think of two reasons for the difference.

  1. Nutrient labels are rounded very aggressively (as in, to the nearest multiple of 10). Thus, doing math on the numbers is likely to result in so much error propagation that any differences are meaningless.

  2. Peanut butter generally does not include the paper skins, whereas roasted peanuts generally do include them. It doesn't seem like a large difference, until you try peanut butter that didn't remove the skins. (Hint: it was awful.)

The differences you see are probably mostly due to reason #1, with maybe a little bit of reason #2 showing through the inherent inaccuracies.

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Great points. Some counterpoints: About point 1 (rounding): Assuming rounding errors, we would still need to explain why the rounding occurs consistently in a way that makes peanut butter 'seem' to contain more protein. If rounding is 'random', then the difference should swing both ways. About point 2, (peanut skin): When looking at peanuts I am only looking at peeled ones. Now there is a point to be made, that food companies are allowed some flexibility, so they might be allowed to put the data for unpeeled peanuts on packaging of peeled peanuts. That might play a role in such a case. – Nikolay Suvandzhiev - sovata Feb 17 at 16:10
    
@NikolaySuvandzhiev-sovata Are you really that sure it's consistent? Generic USDA nutrition facts for peanut butter say 22.2g protein per 100g and for [roasted peanuts] say 24.5g protein per 100g. – Jefromi Feb 17 at 16:19
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@Nikolay, the rounding isn't random, it's just... rounded. It's like one of my favorite T-shirt messages: "2+2=5...for large values of 2". (It works like this: you have a scale that only shows one significant digit. You weigh two things, and each shows 2 on your scale. Now you weigh them together, and your scale shows 5. No, it's not "new math": your two things each actually weighed 2.3, which your scale rounded down to 2. But together, they add up to 4.6, which your scale rounded up to 5.) – Marti Feb 17 at 16:37
    
@Jefromi , I am not sure that the sources I checked (the two I mentioned + a dozen more in other places) are representative, and I would be happy to see other sources that contradict what I found. As dor the USDA source you provided - I am pretty sure it refers to peanut butter that's not just 100% peanuts. The reason I think this is the very high amount of sucrose, which indicates added sugars. So this USDA link probably refers to 'classic' peanut butter, where sugar (and oils, and salt) are added – Nikolay Suvandzhiev - sovata Feb 17 at 16:38
    
@NikolaySuvandzhiev-sovata Ah, you're right, I did look at the wrong one. Thanks for confirming that you looked at a lot; I thought from the question that you'd just looked at one pair. – Jefromi Feb 17 at 16:42

There are at least a dozen varieties of peanuts. Some are better for whole peanuts and others for peanut butter. Possibly there are some nutritional differences between varieties. Also the preparation could come into play, dry roasting vs oil roasting.

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The reason is this; It was shown on an episode of Food Unwrapped. Peanuts are very high in fat but because of how we chew them and swallow we do not break down the structure enough to release all of the fat in them. So when testing fat content for peanut butter the fat content is higher because the nuts are broken down more thus releasing more fat from them. so in fact when people say nuts are fatty and bad for you they aren't actually that bad because you only get about a 3rd of the fat out of them

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While this is interesting, I'm not sure it reflects the way nutrients are actually measured on nutritional labels. Usually the total content is listed from chemical analysis, not based on "how much a human body might be able to absorb in typical digestion." The grinding process doesn't actually change the chemical structure of the peanut butter, so the total fat content listed on the label should be the same. (Also, the cited numbers in the question actually claim LESS fat for peanut butter and more protein.) – Athanasius Feb 18 at 15:38
    
They might be skimming peanut oil off the top after making peanut butter. That'd leave a higher protein/fat ratio in the product. Long ago you'd have to stir your peanut butter to get the peanut oil off the surface and back into the butter, but the big manufacturers have found some way around that problem. – Wayfaring Stranger Feb 19 at 18:15
    
@WayfaringStranger - You still have to stir the peanut butter for 100% peanut butter (which is what the question is asking about). The way "around the problem" is to add some fats that are solid or semisolid at room temperature (since peanut oil isn't). Often some of the peanut oil is removed in the process as well. Up until the past decade, this tended to be done with hydrogenated oils, but "natural" peanut butters in recent years tend to use palm oil or some other fat that's closer to solid at room temperature. – Athanasius Feb 21 at 3:26

Different roasting techniques result in different protein amounts(as per this chart). https://www.healthaliciousness.com/nutritionfacts/nutrition-facts-compare.php

I would also guess that this is a result of the many different types of peanuts> Certain varieties are more likely to be peanut butter and others roasted and eaten by the handful,while other varieties are grown solely to be put into candy bars. However as the chart leads you to believe most of the data for different varieties may be averaged together. Thus, the difference is probably due to specific data for the specific varieties used plus the specific techniques in preparing them.

Also fun fact: oil roasted peanut butter tastes better as Alton Brown has explained in Good Eats and on his blog with youtube videos.

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I am not 100% sure. But as the link you provided for wholefoods states "No... Palm oil" this does not exclude additional peanut oil. Almost every recipe for Peanut Butter I can recall, calls for additional peanut oil.

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In the general case you're not wrong, but that would add fat not protein, and the peanut butter has less fat than the roast peanuts. – Chris H Feb 17 at 19:40
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The link also says, "Ingredients: Roasted organic peanuts (100%)", with no other ingredients listed and that does exclude the addition of peanut oil. – David Richerby Feb 18 at 6:43
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@DavidRicherby, it does not, if the peanut oil was got from Roasted organic peanuts. – Ian Feb 18 at 9:57
    
@Ian Perhaps if the oil was made on-site. I'm pretty sure it would have to be listed from an ingredient, otherwise. For example, yoghurt often lists milk and cream as separate ingredients, despite the fact that cream is "made" by skimming it off the top of milk. – David Richerby Feb 18 at 16:29
    
@DavidRicherby - I think I agree with you that if peanut oil is added, a reasonable person would expect it to be listed as an ingredient. However, it seems likely that what's happening here is the opposite-- that is, more of the non-oil part of the peanut got added (which would explain the higher protein per weight). And since I don't think there's a common word for that part, I'm not surprised if they just blow it off and call it "peanuts". – Don Hatch Feb 19 at 12:14

It could be contamination. The lab tech who measured the peanuts surely would notice an insect or mouse tossed in with his peanuts. Unfortunately, the lab tech who received the peanut butter does not have that luxury. I know that is extremely common with grapes vs raisins. Nearly all commercial raisins have a non-trivial portion of insect matter. Ever thought about how raisins could be "sun-dried" inside?

Admittedly, however, I think it is more likely that some oil is either lost or skimmed off during the process to produce a thicker, less oily product. It also looks like they discard some fiber, probably when it jams the machine.

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