Initial Posting: 8/23/16 Last Update: 5/19/20
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Summary: What You Need to Know About Oat Cereals
- Contamination concern with oats: Oats and oat-based cereals are healthful sources of complex carbohydrates, protein, and fiber, particularly when the whole grain is used. The fiber includes beta-glucan, which can help lower levels of bad cholesterol, reducing the risk of heart disease. However, in the past, some oat-based cereals have been found to be contaminated with ochratoxin A, a potential carcinogen and kidney toxin. (See Background). ConsumerLab.com tested oat-based cereals to find out whether they exceeded contamination limits for this toxin. (See What CL Tested For).
- What about gluten? Although oats don't naturally contain gluten, oat cereals may become cross-contaminated with gluten from wheat products during processing, a potential concern for some people. ConsumerLab.com tested products against the FDA standard for "gluten-free," as well as its own, more stringent "ultra gluten-free" standard (See What CL Tested For).
- Results: Although none of the cereals contained ochratoxin A at a level of concern to adults or older children, testing of one product indicated that it may be best to limit its use by small children. Significant amounts of gluten were found in some products (as much as 95 ppm of gluten). Products labeled "gluten-free" met the FDA standard (no more than 20 ppm of gluten) but not necessarily CL's ultra gluten-free standard (5 ppm) (See What CL Found).
- Which brand? ConsumerLab.com compared products on quality and cost for each category of cereal (steel-cut oats, rolled oats, oat bran, etc.) to come up with its Top Picks.
- Cautions: Although the products tested appear to be generally safe, levels of ochratoxin A may vary over time: be particularly cautious with oat bran products. If you have celiac disease, be aware that some oat cereals contain high amounts of gluten, although this is much less likely if a product is labeled as gluten-free (See Concerns and Cautions).
Background: Benefits and Quality Concerns with Oat-based Breakfast Cereals:
Oats and oat-based cereals are healthy sources of protein and fiber, particularly when the whole grain or oat bran is used. A 40 gram serving of oats provides about 5 grams of protein and 4 grams of fiber -- counted as part of 27 grams of complex carbohydrates, as well as about 3 grams of mono- and polyunsaturated fat. Oat bran provides even more fiber -- about 6 grams per 40 gram serving. The soluble fiber in oats consists predominantly of beta-glucan, which has a cholesterol-lowering effect. In fact, according to the U.S. FDA, foods providing at least 0.75 grams of beta-glucan soluble fiber per serving from oat bran, rolled oats, whole oat flour, or Oatrim (a hydrolyzed oat flour) are permitted to claim that they "reduce the risk of heart disease" as part of a diet low in saturated fat and cholesterol.
However, to get a significant reduction in LDL "bad" cholesterol, you need more than just 0.75 grams of oat beta-glucan. An analysis of 58 studies involving nearly 4,000 middle-aged individuals concluded that about 3.5 grams of oat beta-glucan modestly lowered LDL-cholesterol (-4.2%) and all forms of "bad cholesterol" (-4.8%), as lowering apoB (-2.3%) -- a protein associated with bad cholesterol. The reductions in LDL cholesterol were greater in people with high cholesterol (Ho, Br J Nutr 2016). You can get 3.5 grams of beta-glucan from about 70 grams of whole oats or 50 grams of oat bran, based on dry weights. (A typical serving of either is around 40 grams, dry.)
Increased consumption of fiber, particularly from cereals (such as oats) has generally been associated with a lower risk of colorectal cancer (Song, Gastroenterology 2015). One analysis estimated a 10% reduction in colorectal cancer risk from adding 10 grams of fiber to the diet daily (Aune, BMJ 2011). The risk of death among people with colorectal cancer was also found to decrease with increased fiber intake: A study found that each 5-gram increase in cereal fiber per day was associated with a 33% reduction in death from colorectal cancer and a 22% reduction in death from all causes over an eight-year period. (Each 5-gram increase in daily intake of fiber from vegetables was associated with a 17% decrease in death from all causes, but not colon cancer; fruit fiber was not associated with any decreased risks.) The maximum benefit was at total fiber intake of 24 grams per day (Song, JAMA Oncol 2017).
In addition to the potential benefits from fiber noted above, an analysis of over 240 observational and clinical studies also found significant decreases in the risk cardiovascular-related mortality, the incidence of coronary heart disease, stroke and type 2 diabetes when comparing people with the highest daily intakes of dietary fiber (> 25 grams) with those with the lowest intakes (< 15 grams). Higher consumption of dietary fiber was also associated with lower bodyweight, systolic blood pressure, and total cholesterol. According to the researchers, the findings suggest that adult total dietary intakes of fiber "should be no less than 25 - 29 g per day with additional benefits likely to accrue with higher intakes," (Reynolds, The Lancet 2019). This is in line with the recommended daily value for fiber of 25 grams per day, although the average adult in the U.S. is estimated to consume only 16 grams of fiber per day (CDC 2017).
Oats can be superior to lower-fiber cereals in terms of minimizing increases in blood sugar and insulin levels after consumption. However, this depends on how the oats have been processed. A study among 30 healthy men and women found that after eating equal amounts of different forms of oats prepared according to their label directions (along with 8 ounces of lactose-free milk), the amount of glucose per liter of blood over the next 3 hours was, by far, the lowest with steel-cut oats (72 mmol), followed by old fashion oatmeal flakes (rolled oats) (99 mmol), instant ("quick") oats (107 mmol), and a calorie-equivalent serving of Honey Nut Cheerios (109 mmol). Effects on total insulin followed a similar trend except that instant oats elicited higher total insulin levels, as well as higher peak insulin and glucose levels, than Honey Nut Cheerios. The dramatically lower glucose and insulin responses with steel-cut oats may be due to more of its carbohydrate content remaining unavailable within unbroken plant cells compared to the other forms of oats, while the higher responses with instant oats may be due to its carbohydrate content being more readily available since it is pre-cooked and then pressed (Wolever, Br J Nutr 2019). A separate but similar study by the same researchers evaluated "overnight oats" (rolled oats soaked in skim milk for about 16 hours) and found the impact on blood sugar to be similar to that of steel-cut oats (Wolever, Eur J Clin Nutr 2019). A possible reason why overnight-soaked rolled oats act more like steel-cut oats than cooked rolled oats is that cooking may make the carbohydrate content more available within rolled oats than soaking.
Similarly, a two-week study among 28 men and women with type 2 diabetes showed that blood sugar levels were lower after consuming less processed whole grain products (intact oats, brown rice, and whole-grain bread made with coarsely ground flour and kibbled wheat kernels) than after consuming an equivalent amount of whole grain products providing the same nutritional content, including fiber, but more finely milled (i.e., more processed -- instant oats, brown rice pasta, and whole-grain bread made with finely milled flour). Throughout the study, average increases in blood sugar levels after breakfast and following all meals were, respectively, 9% and 6% lower after consuming the less-processed whole grain products compared to the finely milled products (Aberg, Diabetes Care 2020).
Oats are the basis of many popular cereals including Cheerios, rolled oats (often called oatmeal), steel-cut ("Irish") oats, as well as oat bran. These are all made from oat grains (technically known as groats) processed in different ways. Concern about these products was raised in 2015 when it was reported that 70% of oat-based cereals purchased in the U.S. contained the fungal toxin ochratoxin A, a potential human carcinogen. These results were based on a study by researchers at the University of Idaho who purchased breakfast cereals from local supermarkets in various U.S. cities between 2012 and 2014, testing 489 samples (Lee, J Ag Food Chem 2015). Overall 42% were contaminated with ochratoxin A, with the highest percentage being among oat-based cereals (70%, or 142 out of 203 products), followed by cereals made from wheat (32%), corn (15%), and rice (15%).
Although most of the products in that study contained less than the limit of 3 ng/g (or parts per billion — ppb) of ochratoxin A established by the European Union for processed cereal products (the U.S. has no established limit), 16 of the oat-based cereal products exceeded the limit. Overall, ochratoxin A levels in oat cereals ranged from just 0.14 ng/g to as much as 9.1 ng/g. There was no statistical difference between organic and conventional products. Unfortunately, the researchers did not identify the products by name. Studies conducted in other countries have generally found significant amounts of toxin A contamination in cereal products.
As mentioned above, ochratoxin A is a potential human carcinogen. It is a kidney toxin in all animal species studied and is most likely toxic to humans -- who have the longest half-life for its elimination of any species. It may also have immunosuppressive effects and cause reproductive harm. Unlike some other fungal toxins, the effects will not necessarily cause immediate symptoms. However, excessive urination has been reported -- possibly due to effects on the kidney (Bennett, Clin Microbio Rev 2003).
Ochratoxin A is produced by fungi (mold) which grow on grains (and a variety of other foods including dried fruits and nuts) when exposed to moisture and heat in the field and at various stages of production, storage, and transport. Unfortunately, the toxin is difficult to destroy under normal food-processing or cooking conditions (it is relatively stable even when heated to 392 degrees Fahrenheit).
Ochratoxin A may potentially occur in higher concentrations in oat bran because fungal toxins tend to occur on the external layers of grains, such as the bran, rather than on the on the starchy inner portion or the germ (Vidal, Food and Chem Tox, 2013). All "whole grain" oat products include bran and "oat bran" products will have a higher concentration of bran.
The European Union has proposed a strict tolerable daily intake level for ochratoxin A of 5 ng per kilogram of body weight, which works out to 227 ng of ochratoxin A per 100 lbs of body weight. The amount of ochratoxin A in the most contaminated oat-based cereal tested in the U.S. study discussed above contained 9.3 ng per gram. A single 40 gram serving of this cereal would, therefore, contain 372 ng of ochratoxin A. What this means is that a very small percentage of oat-based breakfast cereals seem capable, on their own, of causing a person to exceed the tolerable daily intake level. The risk, however, is greater for those who consume multiple servings of oat-based cereal per day, are lower in weight (such as children), and/or have significant exposure to ochratoxin A from other sources, such as raisins, which are commonly eaten with oatmeal and used in oatmeal raisin cookies (Palumbo, Lett App Microbiol 2011).
Gluten is of great concern to people with celiac disease, an inflammatory disorder of the small intestine caused by an inappropriate immune response to dietary gluten.
Oats are naturally free of gluten, and therefore, and oat-based foods are often included celiac disease diets. However, this does not mean that all oat products — even those listing just oats as ingredients — are safe for people with celiac disease. Gluten can be found in oat-based cereals which have been produced in facilities handling other gluten-producing grains. Consequently, it is important that gluten-sensitive individuals look for oat-based products which specifically claim to be gluten-free.
Some research suggests that a gluten-like protein in oats called avenin may also cause intestinal inflammation and may be a reason why some celiac patients who eat oats but otherwise adhere to a strict gluten-free diet still experience symptoms (Arentz-Hansen, PLOS Medicine 2004).
Shortly after ConsumerLab completed testing of the products in this Review, a report was published that showed amounts of glyphosate, an herbicide, in oat-based foods. Glyphosate is designed to kill weeds around plants that have been genetically altered to withstand it, such as genetically modified (GMO) soybeans and corn, and it is sprayed on many types of conventional crops such as wheat, oats, and barley prior to harvest as a drying agent and to even-out maturity. Glyphosate is known to cause reproductive toxicity based on animal models, and it may possibly be a carcinogen -- although there is dispute about this. Our anaysis of the reported results indicated that, at standard serving sizes, even foods with the highest known concentrations of glyphosate, such as conventionally grown oats, appear to contain amounts of glyphosate far below those that pose a safety risk or require any type of warning. A serving of Original Cheerios for example, was found to contain 32 mcg of glyphosate, which is far lower than California's warning level of 1,100 mcg and the European adult daily limit of about 34,000 mcg. However, if you are concerned, glyphosate can be largely avoided by choosing organically-grown foods. Be aware that "organic" processed foods, such as cereals, may still contain extremely small amount of glyphosate, likely due to cross-contamination of ingredients.
What CL Tested For:
ConsumerLab.com purchased a variety of processed oat-based cereals from retail stores and websites and tested each for ochratoxin A and heavy metals (which can occur in plant-based products). All products were also tested for gluten, with gluten-free products expected to meet the FDA requirement of no more than 20 ppm. All products were also evaluated to determine if they meet CL's ultra gluten-free requirement (no more than 5 ppm of gluten).