Low Carbohydrate Diet
The goal is to restrict the total carb consumption. Depending on the specific LC plan, individuals start with a daily carb consumption of less than anywhere from 20-50 grams of carbs per day (and only add a few more later when goals are close to being attained). Calories are not important and traditional low carb followers eat mostly fat.
Low Glyemic Index Diet
Total carb consumption is not important. The restriction here is on the type of carbohydrates consumed. The glycemic index is a system of breaking down carbohydrates into ratings based on how strongly each carb affects blood sugar. Ratings of 0-55 are considered low GI, 56-79 are medium, and 80+ are high. People are advised to eat low glycemic foods (you can see a glycemic index chart here). Traditional LGI followers eat a majority of carbohydrates and generally avoid saturated fat. Calorie consumption is important.
A person on a LC diet can eat less than 50 grams of carbs per day while eating foods high on the glycemic index that aren't necessarily carbohydrate-rich (e.g. watermelon). An individual on a LGI diet can eat 300 grams of carbohydrates per day made up of high carb foods with low glycemic ratings (e.g. fettuccine, yogurt, beans).
So...what diet is more effective?
A study performed at Duke University pinned the two nutritional lifestyles against each other for a 24 week period with all obese, diabetic subjects. The LC group consumed unlimited amounts of eggs, poultry, meat, and fish, plus limited amounts of cheese and vegetables. Their diet breakdown was 59% fat, 28% protein, 13 % carbohydrates, and an average of 1,550 calories per day. The LGI group ate their carbohydrates with a glycemic index rating of 55 or less. Their totals came down to 36 % fat, 20% protein, 44% carbohydrates, and 1,335 calories per day. Here are the results (blue highlight is for numbers unhealthy people generally want to raise, red highlight for numbers unhealthy people generally want to decrease, and black is for neutral):
|Low glycemic, reduced-calorie diet group (n = 29)||Low carbohydrate, ketogenic diet group (n = 21)|
|Test||Week 0||Week 24||Week 0 to 24||Week 0||Week 24||Week 0 to 24|
|mean ± sd||mean ± sd||mean change||mean ± sd||mean ± sd||mean change|
|Fasting glucose, mg/dL||166.8 ± 63.7||150.8 ± 47.4||-16.0 *||178.1 ± 72.9||158.2 ± 50.0||-19.9*|
|Waist circumference, inches||47.0 ± 5.1||42.4 ± 5.5||-4.6 *||47.1 ± 5.5||41.8 ± 5.3||-5.3 *|
|Triglycerides, mg/dL||167.1 ± 125.7||147.8 ± 128.5||-19.3||210.4 ± 10.3||142.9 ± 76.9||-67.5 *|
|HDL cholesterol, mg/dL||48.7 ± 11.8||48.7 ± 10.1||-0 †||44.0 ± 8.7||49.6 ± 11.7||+5.6 * †|
|Systolic blood pressure, mmHg||140.8 ± 15.7||130.1 ± 17.1||-10.7 *||144.4 ± 15.0||127.8 ± 13.4||-16.6 *|
|Diastolic blood pressure, mmHg||84.1 ± 11.0||78.5 ± 8.7||-5.6 *||83.9 ± 10.3||75.8 ± 10.9||-8.1 *|
|Body mass index, kg/m2||37.9 ± 6.0||35.2 ± 6.1||-2.7 * †||37.8 ± 6.7||33.9 ± 5.8||-3.9 * †|
|Total cholesterol, mg/dL||190.6 ± 43.8||184.8 ± 45.6||-5.8||191.4 ± 32.0||187.0 ± 35.8||-4.4|
|LDL cholesterol, mg/dL||113.8 ± 40.9||111.0 ± 42.2||-2.8||105.8 ± 25.7||107.1 ± 26.3||+1.3|
|VLDL cholesterol, mg/dL||27.7 ± 13.2||24.4 ± 12.3||-3.3*||37.3 ± 14.9||27.3 ± 15.2||-10.0*|
|Total cholesterol/HDL cholesterol ratio||4.1 ± 1.3||3.9 ± 1.2||-0.2||4.5 ± 1.1||4.1 ± 4.1||-0.4|
|Triglyceride/HDL cholesterol ratio||3.9 ± 3.7||3.3 ± 3.1||-0.6||5.2 ± 3.4||3.4 ± 3.0||-1.8*|
The low carbohydrate group experienced greater improvement in EVERY highlighted category, plus they lost more fat (24.4 lbs. average) than the low glycemic index group (15.2 lbs). Most importantly, the LC group reduced or eliminated medication in 95% of their subjects versus 62% of the LGI group.
Flaws of the Low Glycemic Approach (in my opinion)
- It's impossible to assign specific numbers to the blood sugar affects of specific foods because each individual reacts differently from the next to each food. Corn flakes may invoke a large blood sugar response from some, but a minimal response from others.
- LGI diet doesn't measure the quantity of each food. Eating a pound of a low glycemic index food like yogurt is going to have a different impact on blood sugar from eating four ounces of yogurt, yet they have the same glycemic index rating of 14.
- LGI diet also doesn't account for mixing foods. It's inevitable that a person eats a few foods on the glycemic index in the same meal. When that occurs, how will it be measured?