About Low Carb Diets

Low carb diets are those that severely restrict carbohydrate intake (grains and grain products, milk/yogurt, fruit, sugar, sweets, and starchy vegetables) while allowing greater protein and/or fat intake. Examples of this type of diet include the popular Atkins Diet and South Beach Diet. Although the initial weight loss is exciting and encouraging for many who try low carb diets, research that lasts for more than one-year or more shows that they are no more effective than other eating patterns in helping people lose weight and maintaining weight loss. Research also shows us that low carb diets work by reducing caloric intake. The bottom line is still calories: eat fewer calories than you burn and you will lose weight.

How Low is a Low Carb Diet?

The American Dietetic Association http://www.eatright.org defines low carb diets as those with less than 35% of total calories coming from carbohydrates. For example, carbs would be restricted to 130 grams or less for an intake of 1500 calories. For 2100 calories intake, carbs would be restricted to 184 grams or less.

Specific diets might restrict carbs even more so, especially when the diet is first started. For instance, the Atkins Diet restricts carbs to 20 grams per day for at least the first two weeks of the diet. Even during the maintenance phase, the Atkins Diet restricts carbs to about 60 – 90 grams or so, depending upon whether or not the dieter gains weight with that amount of carbohydrate.

The Institute of Medicine has set the Recommended Daily Allowance (RDA) for carbohydrates at 130 grams per day. This amount is the “average minimum amount of glucose that is utilized by the brain” and is the same for men and women. The RDA for carbs is higher for women who are pregnant or lactating. Therefore, some low carb diets will have a carb intake well below the RDA (e.g. Atkins Diet) and some will not (e.g. 1800 calories intake with 30% calories from carbs = 135 grams).

Benefits with Following a Low Carb Diet

Short-term weight loss

The most obvious benefit to following a low carb diet is the dramatic short-term weight loss without excessive hunger.

Lower blood triglycerides

Low carb diets generally lower blood triglycerides http://www.nlm.nih.gov/medlineplus/triglycerides.html. This is likely due to a reduced intake of refined carbohydrates and sugars as well as a reduction in body weight with low carb diets.

Problems with Following a Low Carb Diet

A number of research studies show that low carb diets are no more effective at long-term weight loss and maintenance of lost weight than other types of macronutrient intake (e.g. low-fat/high carb).

Effect on blood lipids

Weight loss alone can lower total cholesterol, LDL and triglyceride levels. However, weight loss with a diet high in saturated fat intake (e.g., following Atkins Diet without regard to choosing heart healthy foods) can result in increased blood levels of LDL and total cholesterol — both of which are dangerous for heart health. Not all low carb diets are the same. Research does not show that the South Beach Diet causes an increase in harmful blood lipids. This is likely due to the emphasis on heart healthy fats and proteins in the diet.

Dietary Fatigue

Many people start to tire of low carb choices and eventually add carbs back to their diet. This often happens after six-months of following a low carb diet. So, for many of us, low carb eating is not a sustainable long term eating pattern.

Weight regain with carbs

On true low carb diets, dieters naturally consume fewer calories. However, most of us love our carbs and eventually start to include them back into our diet after six months or so. Because we are not in the habit of watching total calories intake, the reintroduction of carbs can cause weight gain by increasing calories intake. This can easily happen if carbs are added back into our diet without adjusting protein and fat downwards to account for the carb calories newly reintroduced. As well, we add a lot of carb calories back into the diet if we have not learned how to choose healthier carbs that are higher in fiber, lower in calories, and learned how to use portion control.

If you are physically active and somehow managed to follow a true low carb diet, then reintroducing dietary carbs could enhance glycogen storage. Both your muscles and liver will store more glycogen with an adequate dietary supply of carbs after training. For every 1 gram of glycogen stored, about 4 grams of water is stored too. This can result in weight gain — but it is not a gain in body fat!


If you have kidney disease of any type, take diabetes pills that increase insulin production, take insulin other than very short-acting or pump (that is, you are not using an insulin: carb ratio), or take any other medication that can decrease blood glucose levels, then you need to discuss the safety of following a true low carb diet with your health care provider before starting.

Physical activity

With true low carb diets, your body gets depleted of stored glycogen in both the liver and muscle. While your brain cells can adjust to using fat metabolites for energy, your muscles are going to give you grief if you engage in endurance aerobic activities or any periodic high intensity activity lasting several minutes at a time (e.g. a soccer game). I strongly encourage those of you who compete in athletics to consider other dietary patterns to meet your long term weight goals and certainly not to continue carb restriction into competition.

Effects on nutrient intake

Low carb diets typically result in a much lower dietary fiber intake. This can cause constipation. Although non-starchy vegetables are high in soluble fibers, they are not so high in insoluble fibers — the type that helps the most with regularity.

Unless you really love non-starchy vegetables and plan to eat a lot of variety and servings of them on your low carb diet, you will be low in a number of nutrients ordinarily provided by carbs such as fruit (dietary fiber, vitamin C, folate, magnesium, and potassium), milk/yogurt/milk substitutes (thiamin, riboflavin, calcium, magnesium, and potassium), dry beans/peas cooked (dietary fiber, thiamin, folate, calcium, magnesium, copper, and potassium), and whole grains (dietary fiber, thiamin, riboflavin, vitamin B6, folate, and magnesium).

If you do not eat red meat, cooked dried beans/peas, or whole grains, then your dietary intake of iron will be quite low. You might need a daily iron supplement.

Although cheese provides calcium with little carb content, it is high in saturated fats unless you buy low fat or fat free versions. Consider a calcium supplement if you eat less than three servings of dairy a day and if you do not eat fish with bones (e.g. sardines). Although there is calcium in vegetable sources, it is not as well absorbed as other forms and is unlikely to meet your daily need.

What If I Prefer Low Carb Eating?

South Beach Diet

If you feel that a true low carb diet is the way to go for you, then consider following the South Beach Diet http://www.amazon.com/South-Beach-Diet-Delicious-Doctor-Designed/dp/1579546463 instead of the Atkins Diet. Although the South Beach Diet is a true low carb diet, it emphasizes heart healthy choices of proteins and fats and has not been shown to increase LDL levels.

Lower carbs vs. low carb

A two-year study conducted in Israel, using a low-carb diet with a special emphasis on plant sources of protein and fats showed continued weight loss and maintenance of weight loss after two years. However, the carb intake varied from 20 grams at the start of the study (Atkins-level induction phase) to about 120 grams by 6 months, with a continued average of about 40% – 41% total calories from carbs during the weight maintenance phase. Technically, by the six-month time period, the study participants were not really consuming a low carb diet although they did consume less than the RDA of 130 grams.

How to count carbs?

Total carbohydrate grams (listed on food labels) include insoluble dietary fiber, soluble dietary fiber, and sugar alcohols (polyols). If you wish, you can use total carbs for your carb counting since it is a more conservative estimate of your digestible carbohydrate intake. That is, using total carbs will in some cases overestimate your true digestible carb load. Public health guidelines use total carbs, not net carbs.

If you are trying to eat a low carb diet and need all the leeway you can get, then counting digestible carbs will allow you to eat more foods that are high in fiber or sugar alcohols. Some food labels list “net carbs” - be aware that the FDA has no legal definition for this term. When you see “net carbs” on food labels, manufacturers are simply subtracting total dietary fiber and sugar alcohol grams from the total carb grams. Therefore, processed foods with these ingredients will tout very low net carbs. These net carb estimates are typically an UNDERESTIMATE of the true digestible carb load since soluble fibers and sugar alcohols can be partially digested and absorbed, and then converted to glucose. To deal with this problem, the American Diabetes Association recommends this formula for carb counting when patients need an accurate estimate of digestible carb grams for insulin dosing:

Total carb grams — (1/2 x total fiber grams when ≥ 5 grams) — (1/2 x total sugar alcohol grams when ≥ 5 grams)

Currently, MyNetDiary calculates net carbs by subtracting total fiber grams from total carbs since sugar alcohols are not currently in the nutrient database. Be sure to look for updates to net carbs and the addition of sugar alcohols to MyNetDiary in the future.

MyNetDiary Works with All Diet Types

MyNetDiary is suited to help you follow any type of macronutrient (carbs, protein, and fat) profile you choose for weight loss. The bottom line is always calories regardless of diet type. If you choose to follow a true low carb diet, then you can see how your diet affects your bottom line intake for calories and other nutrients and correct excesses and deficiencies as needed.

If you do not want to follow a strict low carb diet but would like to experiment with lower carb, higher protein/higher unsaturated fat diets, then you could try setting your carb goal somewhere between 35% - 45% of total calories and then increasing protein and fat intake percentages so that the total percentage is 100%. Of course, with increased protein and fat intake, you will want to be sure that you are not eating too much saturated fat and cholesterol, so you will want to set those goals and track them as well. MyNetDiary Community Forum is an excellent place for members to ask questions about how they could set goals or to simply communicate ideas with other members and me, the dietitian who moderates nutrition-related questions on the Forum.

Parting Thought

Research that is well-conducted has taken some of the mystery out of diets — those that create an energy or calories deficit are those that help people lose weight. So guess what? That pretty much includes all the main diet types — low fat/high carb, low fat/high protein, low carb/high fat and/or high protein. In other words, although as individuals we might have a preference for one eating style over another, in terms of weight loss, anything that creates a calories deficit is going to result in weight loss.

However, along with weight loss, you want to minimize your risk for heart disease. Choosing heart healthy sources of protein and fats will limit your dietary intake of saturated fat and cholesterol. This will go a long way to help you reduce risk for heart disease. For more information on diet and heart disease, please visit the website of the American Heart Association. Also visit the Mayo Clinic’s website on the Mediterranean Diet as this type of diet has also been shown to be extremely heart healthy as well as effective in reducing weight and maintaining lost weight.

If you have questions about this topic, remember that you can post them in MyNetDiary Community Forum.

Katherine Isacks, MPS, RDN, CDE
Disclaimer: Please note that we cannot provide personalized advice and that the information provided does not constitute medical advice. If you are seeking medical advice, please visit a medical professional.

Resources Used For This Article

  • American Dietetic Association: Online Evidence Analysis Library. Low carb diets topic accessed 9/25/09 http://www.adaevidencelibrary.com/default.cfm?auth=1. Link accessible to American Dietetic Association members.
  • Levine MJ, Jones JM, Lineback DR. Low-Carbohydrate Diets: Assessing the Science and Knowledge Gaps, Summary of an ILSI North America Workshop. JADA. 2006; 106: 2086-2094.
  • Miller M, Beach V, Sorkin JD et al. Comparative Effects of Three Popular Diets on Lipids, Endothelial Function, and C-Reactive Protein during Weight Maintenance. JADA. 2009: 109: 713-717.
  • Shai I, Schwarzfuchs D, Henkin Y et al. Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet. NEJM. 359: 229-241. Accessed 9/25/09 with this link. http://content.nejm.org/cgi/reprint/359/3/229.pdf. Link contains letters to the editor and author replies to the article.

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