Toasting bread is a common practice that changes the taste, texture, and appearance of bread. But does toasting bread also change its nutritional value? There are differing opinions on whether toasted bread is healthier than untoasted bread. Proponents argue that toasting improves digestibility and alters the glycemic response. Critics note that toasting can produce harmful compounds. This article reviews the evidence on how toasting affects the nutritional value and health effects of bread.
Does toasting improve digestibility?
Some claim that toasting bread improves its digestibility. When bread is toasted, the starch granules absorb moisture, swell, and gelatinize. This causes structural changes that make the starch more accessible to digestive enzymes.
Several studies have investigated the impact of toasting on the digestive properties of bread:
- One study found that eating toasted bread resulted in a lower glucose response compared to untoasted bread in healthy adults. The area under the glucose curve was 20% lower for toasted bread.
- Another study showed that toasting gluten-free bread significantly increased starch digestibility, breaking down more than double the amount of starch compared to untoasted bread.
- Research in rats found that eating toasted bread led to greater starch digestion and absorption in the small intestine compared to fresh bread.
The enhanced digestibility of toasted bread may be due to structural changes in the starch granules that make them more susceptible to enzyme action. However, more research is needed on the effects of toasting on starch digestion in humans.
Does toasting alter the glycemic response?
The glycemic index (GI) is a measure of how foods affect blood sugar levels. Foods with a lower GI cause a slower, smaller rise in blood sugar compared to high-GI foods.
There is debate around whether toasting affects the GI of bread:
- One study reported that toasting white bread significantly lowered its GI, from a GI of 75 untoasted down to 63 when toasted.
- However, another study found no difference in GI between toasted and fresh white bread.
- Whole grain breads may be less affected by toasting, with one study reporting no change in GI with toasting.
The inconsistent results may be due to differences in study methods and the breads tested. Overall, evidence that toasting lowers GI is limited. More studies controlling for bread type are needed.
Does toasting create acrylamide?
When bread is toasted at high temperatures, a harmful chemical called acrylamide can form.
Acrylamide is classified as a “probable human carcinogen.” It forms when certain foods rich in starch are cooked above 120°C, as in frying, roasting, or baking. High-carb foods like fries, crisps, coffee, and bread are major dietary acrylamide sources.
Studies confirm that toasting bread creates acrylamide:
- Toasting white bread can produce up to 142 micrograms of acrylamide per kg of bread.
- Acrylamide levels increase with higher toasting temperatures and longer cooking times.
- Darker toasting color results in more acrylamide formation.
Minimizing acrylamide in food is important for public health. When toasting bread, aim for the lowest temperature and shortest time needed to achieve palatability and texture.
Does toasting produce antioxidants?
Some sources claim that toasting bread creates antioxidants that provide health benefits.
When bread is toasted, compounds called Maillard reaction products (MRPs) form. These compounds can act as antioxidants to reduce oxidation reactions in the body.
Some research indicates MRPs have antioxidant effects:
- In one study, MRP extracts from toast showed antioxidant activity in the laboratory.
- Acrylamide and other MRPs from toasted bread were able to scavenge free radicals in cells.
- Eating toasted bread increased antioxidant levels in the blood of human subjects compared to fresh bread.
However, the amount of antioxidants produced through typical toasting is likely small compared to eating antioxidant-rich foods like fruits, vegetables, nuts, and whole grains.
More evidence is needed on whether the antioxidant effects of MRPs from toasting produce meaningful health outcomes in humans. The formation of acrylamide likely outweighs any potential benefits.
Does toasting reduce phytates in bread?
Bread contains antinutrients like phytates that can hinder mineral absorption. Some claim that toasting bread reduces phytates.
Phytates are compounds in grains and legumes that bind to minerals like iron, zinc, and calcium and inhibit their absorption.
A few studies have examined the effects of toasting on phytates:
- Toasting bread at 235°C for 3 minutes decreased phytate content by around 25%.
- Higher temperatures (245°C) and longer durations further reduced phytates.
- Toasting alone does not completely eliminate phytates. Additional food processing methods like soaking, sprouting, and fermenting are needed to remove phytates.
While toasting can degrade some phytates, its impact is relatively small. Eating a variety of mineral-rich foods in conjunction with phytate-containing foods can counteract their antinutrient effects.
Does toasting reduce microbes and extend shelf life?
Proponents of toasting note that it can reduce microbes in bread and extend its shelf life. When bread is exposed to high temperatures during toasting:
- Toasting (150°C, 3 minutes) was shown to decrease mold growth compared to fresh bread during storage.
- The bacterial load of bread crumbs was reduced by over 95% following toasting at 150°C for 10 minutes.
- Toasting bread infected with Bacillus cereus spores at 115°C for 4 minutes reduced viability but did not eliminate the spores.
While toasting can lessen microbial load, it does not sterilize bread. Spore-forming bacteria can survive the toasting process. Carefully storing toasted bread and keeping it refrigerated helps prevent microbial growth and spoilage.
Does toasting destroy nutrients in bread?
Critics of toasted bread claim that exposing bread to high heat can destroy beneficial nutrients. However, research on this topic is mixed:
- One study found losses of 7-18% in B vitamins like thiamine, riboflavin, and niacin when bread was toasted.
- Toasting bread did not affect folate levels in multiple studies.
- While some vitamin E loss occurred with toasting, antioxidant activity increased, likely due to Maillard reaction products.
Some water-soluble vitamins like vitamin C and B vitamins are sensitive to heat. However, bread does not contain much of these vitamins to begin with. The nutrient losses with toasting are likely insignificant for most people.
Overall, toasting does not substantially impact the nutrient profile of bread. If consuming toasted bread, pairing it with foods rich in heat-sensitive vitamins can help compensate for any losses.
Does toasting bread increase AGEs?
Advanced glycation end products (AGEs) are compounds that form when proteins and sugars react at high temperatures. Diets high in AGEs have been linked to inflammation, oxidative stress, and chronic disease risk.
Some evidence suggests toasting bread may increase AGE formation:
- Toasting bread increased carboxymethyllysine, a predominant AGE, by 3-4 times compared to fresh bread.
- Higher toasting temperatures and longer duration resulted in greater accumulation of AGEs.
- Acrylamide, which also forms during toasting, can generate AGE compounds during digestion.
Minimizing exposure to AGEs may be prudent for long-term health. Besides limiting toasted foods, using moist cooking methods and avoiding fried foods can reduce dietary AGEs.
Does toasting increase resistant starch?
Resistant starch is a carb that functions like fiber in the body. It resists digestion and provides benefits for gut health and metabolism.
Some studies have assessed whether toasting affects resistant starch levels in bread:
- In one study, resistant starch increased by 2-3 times when bread was toasted compared to fresh bread.
- The amount of resistant starch depended on the original bread type, with rye bread toast containing the most.
- High temperatures during toasting (>150°C) promoted formation of resistant starch.
The higher resistant starch content of toasted bread may result from structural changes to the starch granules that make them less accessible to enzymes.
Increasing resistant starch intake provides health benefits. However, it is unclear if typical toasting conditions would maximize resistant starch to a meaningful degree.
Does toasting gluten-free bread improve quality?
Gluten-free bread often has inferior quality attributes compared to regular bread. Some research shows that toasting can improve the texture of gluten-free bread:
- In gluten-free breads made with rice flour and cornstarch, toasting increased hardness, chewiness, and reduced gumminess.
- Toasting strengthened the crumb structure and lowered rates of staling during storage of gluten-free breads.
- Consumer acceptability scores were higher for toasted gluten-free bread compared to fresh bread.
The changes induced by toasting can make the texture of gluten-free bread more appealing. Toasting may mask some of the differences between gluten-free and gluten-containing breads.
Does toasting alter lectin content in bread?
Some sources claim that toasting bread destroys lectins found in grains. Lectins are proteins that may cause adverse effects in sensitive individuals.
A few studies have looked specifically at the effects of toasting on wheat lectins:
- Toasting bread at 230°F for 3 minutes decreased wheat lectin content by around 30%.
- Higher temperatures further reduced lectins, but did not fully eliminate them.
- Fermentation of dough, as in sourdough bread, lowered lectins more substantially than toasting alone.
While toasting can degrade some lectins, it does not completely remove them. Individuals with lectin sensitivity may still react to toasted bread. Opting for sourdough, sprouted, or traditionally prepared breads may be preferable.
Conclusion
There are pros and cons to eating toasted bread rather than fresh bread. Toasting can increase digestibility, antioxidant activity, resistant starch, and shelf life. However, it also generates harmful compounds like acrylamide and AGEs. While toasting gluten-free bread improves texture, toasting provides minimal benefit for regular bread.
The existing studies comparing toasted and fresh bread have limitations including small sample sizes and lack of long-term clinical data. Overall, there is no conclusive evidence that toasting bread significantly alters its nutritional value or health effects. Moderately toasting bread to enhance texture and taste is likely fine. But overly charring or burning toast to a crisp should be avoided to limit toxin exposure.
As part of a balanced diet, the decision to eat toasted versus fresh bread comes down to personal preference. Focusing on whole grains, fiber, and proper food preparation techniques brings bigger benefits for health.
