Many high-protein, low-carbohydrate diets allow you to eat certain fruits. Depending on the selected diet and current phase, you may be allowed fruits that have minimal impact on blood glucose throughout the duration of the diet. Even one of the strictest low-carbohydrate diet, the Atkins diet, allows fruit after the initial phase. Some low-carbohydrate diets, such as PaNu, allow unlimited fruits throughout. The types and amount of fruits allowed will depend on the diet.
Identification
The reason fruits are not allowed in early stages of some low-carbohydrate diets is that they contain simple sugars that can lead to a rise in blood glucose. Some fruits have a similar impact on blood glucose that eating a tablespoon of sugar would, while others have a far less marked effect. The key difference to how certain fruits affect blood sugar is the glycemic index. According to Oregon State University's Linus Pauling Institute, the glycemic index is a measure of the overall effect a carbohydrate-containing food has on blood sugar. Apples, pears and strawberries are all low glycemic index fruits.
Background
Low-carbohydrate, high-protein diets are based on diets eaten by early man, suggests Protein Power diet designer Dr. Michael Eades. Early humans lived as hunter-gatherers and most likely ate what they could hunt or forage, which was mostly seasonal fruits and vegetables and animal protein. PaNu -- Paleolithic Nutrition designer Dr. Kurt Harris agrees. He says human dietary needs have very likely not evolved beyond those foods, so the widespread availability of processed foods and grain products, as well as the year-round availability of fruits, may be the cause of "diseases of civilization" such as obesity and Type 2 diabetes. By reverting to a Paleolithic style of diet that includes the proteins of ruminant animals, as well as locally in-season fruits and vegetables, your body is able to revert to its natural good health, according to the PaNu website.
Theories/Speculation
Along with the evolutionary theories floated by Eades, Harris and others, "Good Calories, Bad Calories" author Gary Taubes explains that insulin also plays a role in fat metabolism. When you eat high-glycemic carbohydrate foods that cause blood glucose to rise, your pancreas releases insulin into the bloodstream. Insulin's job is fuel usage and storage. When it is present, it moves food into fat storage for later use, and keeps stored fat trapped in fat cells. When insulin isn't present, your body uses its stored fat as fuel, and the result is weight loss. This is why both carbohydrate control and glycemic control are important in low-carbohydrate diets, and why some low-glycemic fruits may still promote weight loss on a low-carbohydrate diet.
Recommendations
The USDA food pyramid recommends eating three to five servings of fruit every day, and selecting fruit from a variety of colors across the color-spectrum in order to get all of the vitamins and nutrients your body needs. Most high-protein, low-carbohydrate diets allow fruits. For instance, while Atkins restricts plant foods to leafy green vegetables during the initial two weeks of the diet, as you progress you are allowed to add a small amount of fruit, starting with berries. The Protein Power diet recommends that you limit the total number of carbohydrates that you eat at every meal to 7 to 10 grams; however, Eades suggests that you can get those carbohydrates from any source including fruits. The PaNu diet allows you to eat fruits when they are locally in season.
Considerations
Since recommendations vary depending on the diet, you may experience more success if you choose a specific diet and carefully follow those instructions. The Mayo Clinic website cautions that low-carbohydrate, high-protein diets are high in saturated fats and cholesterol while being low in fiber, so you may experience an increased risk of heart disease, kidney problems, certain cancers and intestinal disorders.
References
- Oregon State University Linus Pauling Institute: Glycemic Index and Glycemic Load
- "Protein Power Lifeplan"; Michael R. Eades, M.D. and Mary Dan Eades, M.D.; 2000
- PaNu -- Paleolithic Nutrition: What Is PaNu; Kurt G. Harris, M.D.
- "Good Calories, Bad Calories"; Gary Taubes; 2007
- MyPyramid.gov: Inside the Pyramid
- "Dr. Atkins New Diet Revolution;" Robert C. Atkins, M.D.; 1992
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