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"Low-Carbohydrate" Food Facts And Fallacies
"Low-Carbohydrate" Food Facts And Fallacies -- Posted by Gumbo on 10-24-04 14:44
"Low-Carbohydrate" Food Facts And Fallacies
Originally Published:20040701.
Ten years ago, weight-conscious Americans jumped on the fat-free bandwagon.
Supermarket shelves were replete with products touting "reduced-fat" and
"fat-free" labels, which implied that these products were healthier and
lower-calorie alternatives to standard "high-fat" fare. Yet, in the same
10-year time interval, Americans have continued to struggle with
ever-expanding waistlines, gaining an average of 1 lb/year.1 The prevalence
of type 2 diabetes has risen simultaneously.2
Thirty-eight percent of our population is currently attempting to lose
weight.3 The latest trend in the highly lucrative, yet often fickle, diet
industry is a resurgence of low-carbohydrate, high-protein, high-fat diets.
Findings of a February 2004 survey by A.C. Nielsen, a leading market
information company, revealed that 17.2% of households included someone on a
low-carbohydrate diet. Slightly more, 19.2%, included someone who had tried
a low-carb diet but had quit.4 This current diet trend directly counters the
decade-old focus on low-fat diets and implicates carbohydrates as the
culprit in America's obesity problem.
In response to the low-carb resurgence, food manufacturers have rapidly
revised food products and package claims to seemingly reduce the
carbohydrate content of their products and increase consumer demand for
them. Restaurant menus have incorporated purportedly low-carb entrees to
accommodate demand for low-carb meals away from home. Aggressive marketing
schemes imply that these products are healthier alternatives to standard
high-carb fare and that they promote weight loss. For individuals with
diabetes who are counting carbohydrates or attempting to lose weight, the
current marketplace can be a source of a great deal of misinformation, cause
considerable confusion, and possibly affect glycemic control.
Confusing Labeling Terminology
Many food manufacturers have created their own terminology for carbohydrate
content that they claim has minimal effect on blood glucose. They suggest
that consumers subtract carbohydrate contributed from sugar alcohols, fiber,
and glycerin from the total carbohydrate value on the Nutrition Facts panel
of packaged foods to determine the "net carbs," "impact carbs," "effective
carbs," or "net effective carbs" of these foods. While these terms sound
slightly different, they are used by manufacturers to mean essentially the
same thing.
However, this calculation can substantially underestimate the actual
carbohydrate value in many products and may result in insulin errors for
people using carbohydrate counting to determine their insulin dosages. In
addition, individuals with type 2 diabetes following a low-carb regimen for
weight loss may erroneously interpret these "disappearing carbs" to mean
"disappearing calories," as well.
Currently, there are no Food and Drug Administration (FDA) regulations for
the use of carbohydrate claims on food package labels, as there are for
claims about fat, such as "low-fat," "reduced-fat," and "fat-free." Several
organizations, including the Grocery Manufacturers of America, have
petitioned the FDA to establish regulations for carbohydrate content claims.
The FDA is working on guidelines for defining "low," "reduced," or "free"
carbohydrates and for the use of the term "net" in relation to carbohydrate
content of food, based on recent recommendations by its Obesity Working
Group.
The U.S. Department of Agriculture (USDA) Food Safety and Inspection Service
has implemented an interim policy that provides guidelines for the use of
such labels on products within its jurisdiction, such as meat and poultry.
The USDA permits manufacturers to use the terms "net carbs," "impact carbs,"
and "net effective carbs," provided such claims are truthful, not
misleading, and supported by calculations shown on the label.5
The net effect of this labeling lingo is confusion and a host of inquiries
to which health care professionals must respond.
How Do Manufacturers Lower the Carbohydrate Content of Foods?
A few creative chefs have replaced some naturally occurring carbohydrate
with healthy lower-carbohydrate alternatives, such as making
low-carbohydrate mashed "potatoes" with pureed cauliflower. But for the most
part, food manufacturers are lowering the grams of carbohydrate in processed
foods by altering the portion size or replacing naturally occurring
carbohydrate with ingredients that are higher in protein, fat, or other
types of carbohydrate. Examples include:
* substituting soy flour, soy protein, or wheat protein for refined flour
* adding fiber from wheat bran, oat bran, corn bran, inulin, or polydextrose
as a bulking agent
* adding high-fat ingredients, such as nuts and oils
* replacing sugar with sugar alcohols, such as maltitol, lactitol, or
sorbitol, or nonnutritive sweeteners, such as sucralose or acesulfame
potassium
Are the Terms "Net Carbs," "Impact Carbs," and "Net Effective Carbs"
Truthful?
Fiber and sugar alcohols (including glycerin) currently must be included in
the total carbohydrate value shown in foods' Nutrition Facts panel. To
appeal to the low-carb market, food manufacturers are subtracting these
values from the total carbohydrate grams to yield a lower-carbohydrate value
termed "net carbs," "impact carbs," "effective carbs," or "net effective
carbs" (Figure 1). The intent of these claims is to convince consumers that
the products are beneficial to a low-carb diet because with their minimal
effect on blood glucose, increases in insulin levels and consequent weight
gain will not occur.
But is this labeling misleading? Do these alternative carbohydrate values
have a minimal impact on glycemia?
Sugar alcohols/polyols
Sugar alcohols, or polyols, are hydrogenated carbohydrates that are used in
foods primarily as sweeteners and bulking agents. Table 1 provides a list of
commonly used sugar alcohols or polyols and their caloric values. Sugar
alcohols provide 0.2-3.0 kcal/g, rather than the usual 4 kcal/g from
completely absorbed carbohydrate, because they are incompletely absorbed in
the small intestine. FDA regulations require that food manufacturers count
polyols as 2 kcal/g or use the specific kcal/g value determined by the FDA
for a single-sugar alcohol.6 Because of their incomplete absorption,
consumption of polyols can cause flatulence or a laxative effect in varying
degrees in some individuals.
Despite claims by many food manufacturers, sugar alcohols do affect the
postprandial blood glucose response in individuals both with and without
diabetes.7 In some studies, specific sugar alcohols elicited a lower
glycemic response than glucose, fructose, and/or sucrose.7,8 In addition, a
recent study showed maltitol syrup to have a significantly greater glycemic
effect than other sugar alcohols.9
The glycemic effect of sugar alcohols may vary because of the type and
amount of sugar alcohol consumed or because of individual responses. The
American Diabetes Association nutrition recommendations state: "There is no
evidence that the amounts likely to be consumed in a meal or day will result
in significant reduction in total daily energy intake or improvement in
long-term glycemia."10 The following general guidelines11-14 are frequently
used for counseling individuals with diabetes in carbohydrate counting
(Figure 2):
* Subtract half of the grams of total sugar alcohols (polyols) listed from
the total carbohydrate value.
* Many sugar-free products that contain sugar alcohols, such as sugar-free
hard candy and gum, would fall into the "free foods" category, with < 5 g of
carbohydrate or < 20 kcal/serving, making it unnecessary to count the
carbohydrate from the sugar alcohol.
Individuals with diabetes who adjust their insulin based on carbohydrate
intake would be most likely to benefit from this information. However, many
educators are finding the need to address the topic with other patients who
have type 2 diabetes simply because of their interest in the carbohydrate
information on food packages.
Glycerin(e)/glycerol
Glycerin (sometimes spelled glycerine), or glycerol, is a sweet, syrupy
liquid that is about 75% as sweet as sucrose. It is chemically categorized
as a polyol with 4.32 kcal/g. The FDA classifies glycerin as a Generally
Recognized as Safe food additive. As a food additive, glycerin is used in a
variety of products, including nutrition or energy bars, because of its
ability to retain moisture, and reduced-fat frozen desserts, to prevent
formation of ice crystals. Many nutrition bars have > 9 g of glycerin in a
single-serving bar.
According to the FDA, synthetic glycerin is produced by the hydrogenolysis
of carbohydrates15 and must be included in the grams of total carbohydrate
listed in the Nutrition Facts panel. If the label has a statement regarding
sugars, the FDA requires the glycerin content per serving to be declared as
sugar alcohol.16 Some food manufacturers disagree with the classification of
glycerin as a carbohydrate and have been omitting it from their
calculations.
The metabolic fate of glycerin has yet to be determined, but it is believed
to be converted into glucose primarily via gluconeogenesis.17 The effect of
glycerin on blood glucose levels in individuals with diabetes is unknown.
Dietary fiber
The term dietary fiber includes a wide variety of food components, each
having different physiological effects. Dietary fiber is not digested and
absorbed in the small intestine like glucose. Fiber is fermented in the
large intestine to produce fatty acids, which are then absorbed and used as
energy. Foods rich in hemicelluloses and pectins (generally known as soluble
fiber), such as fruits and vegetables, are more completely fermentable than
foods rich in celluloses (insoluble fiber), such as cereals.18 Although the
energy derived from fermented fiber varies among individuals, the estimated
energy yield from fiber is between 1.5 and 2.5 kcal/g.18
Although fiber does contribute to calories, its effect on blood glucose is
likely minimal. For individuals with diabetes who desire this level of
detail, practitioners may suggest subtracting the total grams of dietary
fiber from the grams of total carbohydrate on the Nutrition Facts panel. The
effect is probably insignificant if the amount of dietary fiber is < 5
g.13,14
Do Products Billed as "Low-Carb" Support a Healthy Weight Loss Regimen?
Food products, whether manufactured or naturally occurring, must be
evaluated within the context of the dietary goals they are intended to
support. Therefore, it is essential to evaluate products advertised as
"low-carb" with regard to the contribution they make to weight loss or
maintenance and overall health.
Table 2 compares a purportedly low-carb meal to a more traditional meal
advocated by many professional organizations that promote health. Neither
menu was devised with the intent to restrict calories, because caloric
restriction is not a point of focus for many popular low-carb diets.
Controlled-carb processed products were added to the low-carb meal as
allowable deviations. When comparing the two meals, the following legitimate
reasons for concern about the low-carb claim become apparent:
* The low-carb meal contains less food volume and potentially less satiety
value than the traditional meal.
* The low-carb meal provides ~ 520 more calories and ~ 51 more grams of fat
than the traditional meal.
* Total carbohydrate contained in the low-carb meal is 52 g compared with 83
g in the traditional meal-a difference of 31 g.
* Of the 52 g of total carbohydrate in the low-carb meal, 17 g are claimed
to be "net carbs." The other 35 g (27 of which are from the controlled-carb
products) seem to be negated.
Individuals with diabetes should be advised that use of low-carb products
does not necessarily lead to weight loss or improvements in metabolic
measures.
Implications of the Low-Carb Diet Trend
History tells us that popular diets, like fashion trends, tend to cycle. The
currently fashionable low-carbohydrate diet trend has experienced periods of
more and less popularity during the past 40 years. Unfortunately, this diet
trend promotes misconceptions about carbohydrates and can cause people to
restrict health-promoting nutrients while guiding them to consume liberal
amount of nutrients, especially saturated fat and cholesterol, that can
negatively affect health.
Perhaps the greatest risk of this diet trend is the impact it may have on
eating behaviors of those individuals who have been unable to establish
sensible relationships with food. Manipulations in food manufacturing and
terminology that seemingly allow undesirable nutrients and, by association,
their calories to magically disappear are psychologically appealing to
dieters who are rationalizing how to eat more without having it count.
Individuals with diabetes should be offered sound guidance about how to
interpret truths and mistruths of any diet trend. This is crucial within the
context of the low-carb trend because claims about the glycemic effects of
carbohydrate foods and their contribution to insulin
resistance/hyperinsulinemia and weight gain tend to be a central
philosophical feature. Confusing labeling lingo that has been contrived and
printed on packages of manufactured foods can create unique challenges for
individuals with diabetes who must accurately count grams of carbohydrate to
achieve glycemic control, particularly individuals on intensive insulin
therapy.
In truth, the rise in prevalence of overweight and obesity can largely be
attributed to energy imbalance resulting from an increase in energy intake
and decrease in energy expenditure-not to the excessive intake of any single
nutrient.19 Diets that support severely restricting or omitting any single
nutrient without offering psychosocial support and monitoring of metabolic
parameters should be considered suspect. Severely restricting or omitting
carbohydrates can have potential negative long-term health consequences,
especially if healthful carbohydrate sources, such as fruits, vegetables,
whole grains, and dairy foods, are severely restricted.
Thus, not only amounts, but also sources of carbohydrate should be a focus
of any discussion about meal planning.7 Highly processed grains, cereals,
and sugars should be replaced with minimally processed whole grains, fruits,
vegetables, and dairy foods for optimal nutritional benefits. Sweets and
sugars should be used with moderation, especially for those who need to lose
weight. When these sensible, but not headline news-making, guidelines are
applied, use of highly processed and manufactured foods that manipulate
carbohydrates becomes unnecessary.
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