Low-Carb Diets

If we only had a dollar for every time someone asked about the low-carbohydrate diet! In the world of "all or nothing," the carbohydrate issue has many sides. Because of the confusion and strongly-held opinions, this Tidbit will try to provide some facts.

The first Recommended Daily Allowance (RDA) for carbohydrates was made by the Institute of Medicine (IOM) Food and Nutrition Board in 2002.1 The IOM determined that the RDA for carbohydrate consumption is 130 grams per day for children and adults. In reviewing IOM's lengthy rationale, I was reminded of a few helpful facts:

  • Fat, carbohydrate and protein substitute for one another, to some extent in meeting the body's energy needs.
  • The only cells that have an absolute requirement for glucose as an oxidizable fuel are those of the CNS (i.e., the brain). During prolonged starvation, the body adapts and uses ketones for energy.
  • Adaptation to a fat and protein fuel requires considerable metabolic adjustment.

Some other interesting facts:

  • Most low CHO meal plans (i.e., Atkins, South Beach) allow for 20 to 50 grams of CHO per day in Phase I and increase the carbohydrate allowance to 75 to 100 grams per day in subsequent phases.
  • There is no official definition of a "low-carbohydrate" diet. Many "diets" which claim not to be low-carbohydrate actually are below the RDA of 130 grams per day.
  • Most people get far more than 130 grams of carbohydrates per day. IOM estimated the median intake is 180 to 330 grams per day.
  • If one calculates how many carbohydrates are consumed in a hypothetical day . . .
    • Doughnuts and sweet coffee for breakfast
    • A super-sized fast food meal with soda for lunch
    • Cookies for a snack
    • Spaghetti with sauce, salad, and garlic bread for dinner
    • Ice cream for a bedtime snack

. . . the grams of carbohydrates quickly reach the 400 to 500+ level!

  • Some health conditions are exacerbated by too many carbohydrates. Dr. Reaven, a UCLA researcher who has done extensive research on metabolic syndrome and insulin resistance, suggests that someone with metabolic syndrome limit his or her carbohydrate intake to 40% of calories consumed versus the usual recommendation of 50 to 60%. This equates to around 220 grams of carbohydrates per day for someone eating 2200 kilocalories per day.

So what is a health professional to suggest when asked about any new diet being promoted? The evidence supporting healthy eating, at this time, includes these components:

  • The body needs all kinds of chemicals, which it gets from food, to do its work. Choosing a variety of foods, including carbohydrates (or whatever the fad diet is bashing), is important.
  • Choose whole grains and whole grain products over highly-processed carbohydrates.
  • Choose healthy fats—those that contain primarily mono- and polyunsaturated fats versus saturated fats.
  • Choose plant-based proteins, such as legumes, nuts, and soy as much as or more than lean animal-based proteins.
  • Eat fruits and vegetables in abundance, and limit highly-processed drinks and snacks.
  • Eat at regular intervals (about every 4 to 6 hours during waking hours).
  • If patients choose to go on a low-carbohydrate diet, suggest that when they feel weak, shaky, mentally compromised, etc., they should check out their carb intake — it may be too low, causing their symptoms.
  • As with everything else, moderation is the key. One can get too few carbohydrates, or too many.

For more information on healthy eating and low-carbohydrate diets, try the following resources:

  • Ornish D. Was Dr. Atkins right? J Am Diet Assoc. 2004;104:537-42.


  1. Panel on the Dietary Reference Intakes for Macronutrients, Institute of Medicine. Dietary reference intakes for energy, carbohydrates, fiber, fat, fatty acids, cholesterol, protein, and amino acids. Washington, DC: National Academies Press, 2002