Nuts are nutritious foods that provide healthy fats, fiber, vitamins and minerals. However, there has been some debate about whether the calories from nuts are fully absorbed by the body. This article will examine the research on nut calories and absorption.
Quick Answers
– The body does not absorb all the calories in nuts – estimates range from 5-15% of calories being excreted rather than absorbed.
– Factors like nut variety, processing method, and individual differences affect absorption.
– Chewing thoroughly helps break down nut cell walls so calories can be absorbed.
– The healthy fats, fiber and plant compounds in nuts enhance satiety and offset some calorie absorption.
Do our bodies absorb all the calories in nuts?
In a nutshell, no – our bodies do not absorb 100% of the calories that nuts contain. However, the percentage of calories absorbed can vary based on factors like nut type, nut form (whole vs processed), food matrix, and individual differences in physiology and gut bacteria.
Most nuts are high in fat, containing 150-200 calories per ounce. But estimates suggest our bodies only absorb around 80-85% of those calories. Some studies show an even wider range of 5-15% of calories being excreted from nuts:
- One study found that about 18% of the calories from pistachios were not digested or absorbed.
- Research on almonds showed 5-15% of calories were excreted through the feces.
- Studies on peanuts estimate up to 16% of calories are lost through fecal fat excretion.
What accounts for these missing calories that our bodies don’t absorb from nuts? Let’s take a deeper look at some of the factors at play.
Factors That Impact Nutrient Absorption from Nuts
There are several reasons why our bodies may not fully absorb all the calories found naturally in nuts:
1. Cell walls and fiber content
Nuts are surrounded by rigid plant cell walls. Some of these cell walls escape digestion, limiting the bioaccessibility of lipids and other nutrients within the nutmeat. The more intact the nut’s cell walls remain as they pass through our digestive tract, the fewer calories our bodies are able to absorb.
Chewing thoroughly helps break down cell walls, enabling more nutritional components to be released and absorbed. But some intact cells invariably make it through our digestive systems.
The fiber content of nuts may also play a role. While fiber provides many health benefits, it can also bind to lipids and limit their absorption. Fecal analysis shows a portion of fat from nuts is excreted bound to dietary fiber rather than being digested.
2. Nut variety and form
Nut structure and density impacts how thoroughly we chew and digest them, which then affects calorie absorption. For instance, pistachios have rigid cell walls that yield greater intact cells passing through digestion compared to other nuts. This partly explains why pistachios have shown some of the highest recorded fecal fat losses.
Processing methods also make a difference. Nut butters and oils lead to much higher calorie absorption than whole nuts. One study found that 97% of the calories from peanut oil were absorbed, compared to 80-85% of calories from whole peanuts.
Calorie absorption varies between nuts from 93% for macadamia nuts to 76% for almonds. Each nut variety has a unique combination of protein, fiber, and phytochemicals that impacts its digestibility.
3. Food matrix effects
How nuts are consumed along with other foods can potentially change how many calories are absorbed. One study found that adding almonds to bread reduced calorie absorption from the almonds compared to consuming almonds alone. The bread matrix seemed to partly obstruct the bioaccessibility of the nut lipids.
More research is needed on matrix effects from different food pairings. But the available evidence suggests combining nuts with other foods may slightly reduce the calories that can be absorbed compared to eating nuts alone.
4. Gut bacteria
Recent research indicates the digestive enzymes and gut microbiome of an individual may impact calorie absorption from nuts. We each host a unique set of gut microbes that influence how efficiently we can metabolize and absorb nutrients from food.
In one small study, subjects were fed identical almond meals on 3 occasions. There was substantial individual variability in the calories absorbed from the almonds, ranging from 70 to 99%. around 8% of this variability was linked to differences in their gut microbiota composition.
More research on the gut microbiome’s role is needed. But this suggests personal differences in our digestive bacteria may partially account for varying degrees of calorie absorption from nuts between individuals.
Mechanisms for Malabsorption of Nut Calories
Several interconnected mechanisms explain why some calories from nuts go undigested and get excreted rather than absorbed in our GI tracts:
Limited Bioaccessibility
Bioaccessibility refers to the amount of nutrients freed from a food matrix that are available for absorption in the GI tract. The rigid plant cell walls in nuts reduce bioaccessibility of the intracellular fats and proteins. Without chewing thoroughly, some of these cells remain intact and exit the body undigested.
Fecal Fat Loss
Indigestible cell walls and intrinsic nut fiber lead to a portion of the fat in nuts being excreted in feces. One study measured a 10.2% fecal fat loss from whole almonds. Measurable amounts of fat are lost through feces after eating different nuts.
Increased Metabolism
There is some evidence that consuming nuts may boost your metabolism slightly as part of the thermic effect of food. In one study, resting energy expenditure increased by 11% after subjects ate about 2 ounces of nuts per day for 19 weeks.
A revved up metabolism could theoretically allow your body to burn a small amount of extra calories after eating nuts.
Fat Malabsorption
Malabsorption refers to an impairment in the ability to digest and absorb nutrients. Some malabsorption of fat from nuts may occur due to the previously discussed issues with bioaccessibility and intact nut cells getting excreted.
Satiety Effects
Nuts are very satiating foods due to their protein, fiber, and unsaturated fat content. Eating nuts leads to increased signals of fullness compared to other snacks. This satiety effect may cause unconscious reduction in calories consumed at later meals after eating nuts, partially offsetting the calories within nuts.
Health Benefits Beyond Calorie Content
When considering the calorie content of nuts, it’s important to note their significant health benefits as well:
- Heart health – Nut nutrients like unsaturated fats, fiber, antioxidants, arginine, and minerals benefit cardiovascular health markers.
- Blood sugar – Despite their high fat content, most nuts have low glycemic impact and help regulate blood sugar levels.
- Satiety – Appetite regulating hormones and other satiety signals make nuts filling snacks that curb hunger.
- Weight control – Clinical trials link regular nut consumption to slightly lower BMI and weight compared to not eating nuts.
- Gut health – Compounds like polyphenols feed beneficial gut bacteria. The fiber in nuts also promotes a healthy microbiome.
In one large study, people who regularly ate nuts had a 39% and 52% lower risk of fatal heart disease and diabetes respectively compared to those who rarely ate nuts. Their lifespans were also about 2 years longer on average.
So despite their high calorie density on paper, nuts are associated with anti-obesity and anti-diabetes effects, likely due to their ability to reduce chronic disease risk factors.
Tips to Maximize Nutrient Absorption from Nuts
Here are some practical tips to help you absorb the most nutrients possible from your nut intake:
- Chew nuts thoroughly – at least 10-15 chews per nut can help grind down cell walls so your GI enzymes can access more fat and protein.
- Limit intake of nut butters and oils – the high bioaccessibility increases calorie absorption compared to whole nuts.
- Pair nuts with fiber-rich foods – additional fiber may reduce total calories absorbed by binding to nut fats.
- Consume a variety of nuts – rotating different nuts like almonds, walnuts, and pistachios can provide a mix of protein, fats, and phytonutrients.
- Account for your individual satiety response – nuts may help you feel full and naturally eat less at other times.
The Bottom Line
Current evidence shows our bodies do not absorb all the calories provided by nuts. We pass a portion of these calories through feces undigested. However, the amount of calories lost through malabsorption varies substantially based on nut characteristics, processing method, food matrix, and individual gut microbiota.
Chewing thoroughly and choosing various whole nuts over nut butters can help reduce calorie absorption. But the significant cardiovascular and metabolic benefits of nuts outweigh the need to minimize absorbed calories for most healthy people.
Nuts are a healthy plant-based protein and fat source that provide satiety, heart-healthy fats, and an array of vitamins, minerals, and antioxidants. The bioaccessible calories we do absorb from nuts come packaged with many protective compounds linked to better health outcomes.
