People who eat a low carb or ketogenic diet often ask about calculating “net carbs” and are surprised by my reply, as it differs from what they’ve read online. The commonly held advice is to subtract “fiber” from the total amount of carbohydrate on the label to arrive at “net carbs” can lead to an underestimation of nutrient intake, as well as possibly an underestimation of the effect of the food on blood glucose and insulin release when those foods are processed into other foods by grinding and/or heating.
As with other evidence-based meal patterns, a “whole foods” approach when following a low-carb lifestyle, is preferable. That doesn’t mean that people shouldn’t enjoy the occasional low-carb treat, as long as they understand that a baked good prepared from almond flour is not equivalent in terms of nutrient availability to the whole almonds from which it is made.
“Net Carbs” and the Perils of Food Processing
In a two-part series of articles posted in March 2018 on my dedicated low-carb website that were titled The Perils of Food Processing, I showed that both the amount and type of food processing applied to a food impacts the amount of nutrients available for absorption by the body, as well as having varying effects on the body’s insulin and blood sugar response.
“Food processing” in this context means that amount that a food undergoes cutting or grinding and/or cooking in some way, including baking.
Mechanical processing, such pounding or grinding food is an ancient form of food processing which has an effect on how many nutrients are available to be digested. That is, the nutrients available to the body when food is eaten raw and whole versus raw and pounded is significant, and this holds true whether the food is animal protein such as meat or a starchy vegetable such as sweet potato. It is also true for foods such as almonds.
The availability of carbohydrate and energy is different for whole, raw almonds versus ground almonds such as almond flour — a staple in low carb and keto baking. More on that, below.
Changes in Insulin and Blood Glucose Response Resulting from Food Processing
As covered in the first article linked to above, mechanical processing of a food doesn’t change the amount of carbohydrate that is in it. That is, when we compare 60 g of whole apple with 60 g of pureed apple or 60 g of juiced apple, there is the same amount of carbohydrate in each. The Glycemic Index of these three are very similar so this isn’t very helpful to inform about the blood glucose response to actually eating these different foods.
When these foods are eaten, the insulin response and blood glucose response 90 minutes later is significantly different.
As can be seen by the graph on the right, in healthy individuals blood insulin level goes very high with the juiced apple and in response, blood glucose then goes very low, below baseline. The response seen with the juiced apple is typical of what is seen with ultra-processed carbohydrates.
The same effect that is true for fruit is true when grain is ground; plasma insulin response increases the smaller the particle size of the grain.
Whole grain releases less insulin than the same amount of cracked grains, which is less than the same amount of course flour. The highest amount of insulin is released in response to eating the same amount of fine flour.
What is true for wheat is also true for rice and of interest, there isn’t a big difference between the insulin response with brown rice versus white rice.
While there is no difference in the Glycemic Index or Glycemic Load of whole wheat versus ground wheat or whole rice versus ground rice, there is a huge difference in the insulin response with difference types of mechanical processing.
Also as outlined in the previous articles (links above), the amount of fiber that was in the grain did not make a difference in the amount of insulin released, only the amount of mechanical processing of the grain. So, eating brown rice versus white rice won’t change the amount of insulin that is released.
Remember, insulin is a hormone that signals the body to store energy (calories), so increased insulin response in response to grinding food is important.
In short, it is the amount of cell disruption caused by grinding that increases insulin and glucose response; not the specific amount of carbohydrate in the whole food, nor the amount of fiber in the food.
For those with Type 2 Diabetes or pre-diabetes, applying “net carb” calculations to foods that have been ground is a problem; as it does not take into account the increased insulin release and resulting change in glucose response, as well as the change in energy availability caused by the grinding.
NOTE (June 2 2019): The fiber in the whole food and the ground food remains unchanged and is indigestible by the body, although it is digested by the gut microbiome into fatty acids. While fiber may slow the gastric emptying of the ground product (compared to the same product with the fiber removed), in and by itself the presence of fiber in the ground product compared to the whole food does not reduce the impact on insulin and glycemic response that the grinding causes.
The Effect of Cooking on Nutrient Availability
Also as documented in the first of the two articles on food processing, cooking also has an effect on nutrient availability. When grains are cooked they become much more digestible — meaning that more of the nutrients are available to be absorbed. In the case of potatoes, there is double or triple the amount of energy (calories) available to the body when they are cooked versus when they are raw and these calories are now available to the body where they weren’t when they were raw.
When foods that are high in fat (lipid) such as peanuts are cooked, the amount of energy the body is able to derive from the food, increases.
Does Food Processing Affect Almonds?
Yesterday, in preparing to write this article, I was curious if there was any information available specifically about almonds as almond flour is used in most low-carb and “keto” baked goods.
I went looking and found a September 2016 article in the International Journal of Food Science and Technology titled “A review of the impact of processing on nutrient bioaccessibility and digestion of almonds” [1] which documents the most common processing technique used on almonds and their effect on the digestion of nutrients.
In short, lab studies and animal and human studies demonstrate that there are marked differences in the way various forms of almonds (whole raw, whole roasted, blanched, milled flour) are digested and the amount of different macronutrients that are absorbed.
What is true with grinding grain, apples and peanuts holds true for almonds.
It is reasonable to assume that the body’s release of insulin and the corresponding glucose response is similarly changed by the increased bioavailablity of nutrients in those processed foods.
Ultra-processed foods, whether fruit, grains, or nuts are not treated by the body the same as whole, unprocessed foods. The macronutrient availability (i.e. amount of carbohydrate and energy) in whole, unprocessed foods is not the same as in the same foods that have been ground and/or heated, and the amount of insulin released and glucose absorbed can differ too.
Final Thoughts on “Net Carbs”
One cannot simply subtract the fiber that is contained in the whole, unprocessed food from the total carbohydrate content of the processed food and arrive at “net carbs” because the amount of macronutrient absorption of the food is increased due to the cell disruption of grinding and heating. For those with Type 2 Diabetes or pre-diabetes, one also needs to factor in the differential impact on insulin and blood glucose release that results from the food processing.
One can subtract the fiber in whole, raw almonds and arrive at “net carbs” on the assumption that the fiber is indigestible by the body and that the other nutrients listed on the label apply to the food in it’s current form, but roasting and grinding those same almonds into almond butter or grinding those almonds into almond flour and then baking (i.e. cooking) them into a host of low carb or keto ‘treats’ on the basis of their low “net carb” content can significantly underestimate their total macronutrient content.
Should one choose to use the idea of “net carbs”, it should be applied only to whole, unprocessed (not ground or heated) foods.
Ultra-processed foods, irrespective of the carbohydrate content of the original whole, unprocessed foods from which they are made are not equivalent in nutrient availability or the body’s response to them as to whole, unprocessed foods.
While low-carb and keto ‘treats’ may be nice as “sometimes foods”, they are not ideal as “everyday foods” if weight loss and lowering blood glucose and insulin response are goals.
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To your good health!
Joy
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Reference
- Grundy MM, Lapsley K, Ellis PR. A review of the impact of processing on nutrient bioaccessibility and digestion of almonds. Int J Food Sci Technol. 2016;51(9):1937—1946. doi:10.1111/ijfs.13192