Popular diet books have long recommended limiting particular types of macronutrients — usually carbohydrate or fat — to bring about weight loss and improve overall health. Some have additionally encouraged an increased intake of protein, the third type of macronutrient in the human diet, for the same reasons. While not all popular diet books address diabetes, many suggest that their recommendations can help with blood glucose control as well as weight loss.
At the same time, respected health organizations such as the American Diabetes Association (ADA) and the Joslin Diabetes Center have also published dietary guidelines for people with diabetes or prediabetes. (In prediabetes, blood glucose levels are higher than normal but not high enough for a diagnosis of diabetes. Having prediabetes raises the risk of developing Type 2 diabetes.) Both recommend weight loss for people who are overweight and give suggestions for losing weight.
Diet and weight loss are relevant topics for people with diabetes, since what you eat affects blood glucose control — not to mention blood pressure and blood lipid (cholesterol and triglyceride) levels — and losing excess weight can improve diabetes control and overall health. But with all the different books and guidelines out there, it can be difficult for the average person to know which eating plan might really have the desired effects while minimizing undesired effects such as feelings of chronic hunger.
In the interest of determining whether there are any truths to the claims that restricting or increasing the proportion of a particular macronutrient in the diet is beneficial, researchers have in recent years been testing various diets. Among the questions asked by researchers are whether following a particular diet leads to weight loss, a change in the proportion of body fat to muscle, improved cholesterol levels, lower triglyceride levels, lower blood glucose levels, and lower insulin resistance (which should lead to better blood glucose control).
This article examines some of the research that’s been done on diets with varying macronutrient composition. It also reviews the current nutrition recommendations of the ADA for all people with diabetes and those of the Joslin Diabetes Center for overweight people with either Type 2 diabetes or prediabetes.
According to the ADA, medical nutrition therapy (more commonly referred to as “meal planning”) for diabetes should aim to achieve and maintain the following:
- Blood glucose levels in the normal range or as close to normal as is safely possible
- Cholesterol and triglyceride levels that reduce the risk for vascular (blood vessel) disease
- Blood pressure levels in the normal range or as close to normal as is safely possible
In addition, a person’s meal plan should be designed to prevent or slow the rate of development of chronic complications of diabetes, address individual nutrition needs, and maintain the pleasure in eating.
While the ADA does not recommend specific proportions of carbohydrate, fat, and protein in the diet, it does recommend the following for preventing Type 2 diabetes in adults who are at high risk of developing it:
- Reducing calorie intake
- Consuming at least 14 grams of dietary fiber per 1,000 calories per day
- Making half of grain choices whole grains
- Consuming low-glycemic foods that are rich in fiber and other nutrients (The glycemic index is a measure of how a food affects blood glucose levels following meals. Foods with a low glycemic index raise blood glucose levels less or more slowly than foods with a high glycemic index.)
For managing diabetes, the ADA offers the following recommendations regarding the various macronutrients:
Carbohydrate. Consumption of carbohydrate-containing foods such as fruits, vegetables, whole grains, legumes, and low-fat milk is encouraged. Consuming less than 130 grams of carbohydrate per day is not recommended for diabetes management. Counting the total amount of carbohydrate consumed is recommended for blood glucose control; choosing foods with a low glycemic index may provide additional benefit in controlling blood glucose. Eating a variety of fiber-containing foods is recommended.
Protein. There’s no reason for people who have diabetes and normal kidney function to consume other than the usual protein intake of most Americans, which is 15% to 20% of total daily calories. High-protein diets are not recommended for weight loss because their long-term effects are unknown.
Fat. Saturated fat should be limited to less than 7% of total calories, and intake of trans fat should be minimized. Two or more servings of fish per week are recommended to provide omega-3 fatty acids.
Cholesterol. Dietary cholesterol should be limited to less than 200 milligrams per day.
The goals of the Joslin Diabetes Center guideline for overweight and obese adults with Type 2 diabetes or prediabetes are basically the same as the ADA’s goals: improve cardiovascular health, control blood glucose levels, and reduce body fat. However, unlike the ADA, they do recommend a particular distribution of macronutrients. Specifics of the Joslin guideline are as follows:
Carbohydrate. About 40% of calories should come from carbohydrate. Like the ADA, however, Joslin recommends consuming no less than 130 grams of carbohydrate per day, which means that people with very low calorie intakes may end up getting slightly more than 40% of their calories from carbohydrate.
The Joslin guideline states that when choosing carbohydrate-containing foods, preference should given to foods with a low glycemic index. Recommended carbohydrate foods include fresh vegetables, fruits, beans, and whole or minimally refined grains. At least 20–35 grams of fiber should be consumed daily.
Protein. About 20% to 30% of calories should come from protein, unless a person has any signs of kidney disease, such as the presence of protein in his urine. (People with diabetes are generally advised to have a microalbuminuria test once a year to check for this.) Recommended protein sources are fish, skinless chicken or turkey, nonfat or low-fat dairy products, legumes (dried beans and peas), tofu, tempeh (a soy product), and seitan (wheat gluten).
Fat. About 30% to 35% of calories should come from fat, primarily monounsaturated and polyunsaturated fats. Saturated fat should be limited to less than 10% of calories or less than 7% in people with LDL cholesterol over 100 mg/dl. Recommended fat sources include olive oil, canola oil, nuts, seeds, and fatty fish such as salmon.
Cholesterol. Dietary cholesterol should be limited to less than 300 milligrams a day or less than 200 milligrams in people with LDL cholesterol over 100 mg/dl.
Since the Joslin guideline was written for people who are overweight or obese and weight loss is one of the primary goals, calorie reduction is also part of the plan. Daily calories should be reduced by 250 to 500, and total daily calorie intake should be no less than 1,000–1,200 for women and no less than 1,200–1,600 for men.
What the research shows
As mentioned earlier, researchers have in recent years been testing various diets with differing proportions of carbohydrate, fat, and protein to see whether and how they affect the body differently. In many if not most cases, the number of calories that study participants consume is restricted, and when that is true, participants tend to lose weight no matter what the composition of their diet. Indeed, higher-protein, lower-carbohydrate diets do not consistently cause more weight loss than lower-protein, higher-carbohydrate diets.
However, higher-protein, lower-carbohydrate diets may nonetheless offer certain benefits, such as lower triglycerides (the most abundant type of blood fat), a higher high-density lipoprotein (HDL, or “good”) cholesterol level, loss of more body fat, maintenance of more lean body tissue, and less hunger while restricting calories.
Less hunger. Researchers at Arizona State University had 20 healthy adults follow one of two diets. Both diets restricted the number of calories per day, and both got less than 30% of calories from fat. However, one got 15% of calories from protein, and the other got 30% of calories from protein. After six weeks, both groups reported an average weight loss of 6% of body weight and a similar decrease in fat mass. However, in the first month of the study, the people with the higher protein intake reported more satisfaction and less hunger.
Lower body fat and triglycerides. A 12-week study completed in Australia had 100 overweight women follow calorie-restricted, low-fat diets. One group had a higher protein intake, and one a higher carbohydrate intake. Both groups lost similar amounts of weight. But among the women with high triglycerides, those who ate a higher-protein diet lost significantly more body fat than those who ate a higher-carbohydrate diet. The women who ate more protein also experienced a significantly greater decrease in triglycerides.
More initial weight loss. A one-year study compared the weight loss achieved through following a low-carbohydrate, high-protein, high-fat diet (based on the Atkins diet) with that achieved through following a low-calorie, high-carbohydrate, low-fat diet (containing about 60% carbohydrate, 15% protein, and 30% fat). The group that followed the Atkins diet was instructed to limit carbohydrate to 20 grams per day for the first two weeks, then increase that amount gradually. They were not instructed to limit protein or fat.
The study participants were 63 obese men and women. After 3 months, the Atkins diet group had a greater weight loss (6.8% of body weight lost), and after 6 months, the Atkins diet group again had a greater weight loss (7.0% of body weight lost). After 12 months, however, the weight loss between groups was not different.
The authors concluded that a lower-carbohydrate diet produces greater weight loss in the early stages, but that difficulty following such a plan may result in total amount of weight loss after 12 months being no different from the weight loss achieved with a higher-carbohydrate diet.
Lower triglycerides, higher HDL. Two studies conducted by researchers at the University of Illinois reported that when consuming a diet with a higher proportion of protein, people experienced significantly greater decreases in triglycerides, as well as greater maintenance of high-density lipoprotein (HDL, or “good”) cholesterol.
Less body fat. A study conducted in Australia followed 54 obese men and women with Type 2 diabetes over an eight-week period. All participants consumed about 1,600 calories per day, but one group’s diet consisted of 55% carbohydrate, 16% protein, and 26% fat (the lower-protein diet), and the other’s had 42% carbohydrate, 28% protein, and 28% fat (the higher-protein diet). After eight weeks, the total amount of weight lost was similar between groups. However, men lost more weight on the lower-protein diet, while women lost more weight on the higher-protein diet. Additionally, women who followed the higher-protein diet lost almost two times more body fat than women who ate more carbohydrate, but no such differences in body fat were found in men.
In another study, this one conducted in Illinois, 24 women aged 45–56 years were assigned to either a higher-protein or a lower-protein diet for 10 weeks. While the two groups lost about the same amount of weight, the women who ate more protein experienced significantly greater loss of body fat.
While weight loss may be the most important goal for people following a diet, the actual changes in body composition — or proportions of fat to muscle — are more important for your health. Excessive body-fat stores, especially fat stored in the abdomen, are strongly linked to obesity, diabetes, cancer, and cardiovascular disease.
Glucose and insulin levels
Finding the right meal plan is not just important for achieving and maintaining a healthy weight; it’s important for blood glucose control as well. Some studies have investigated whether a higher-protein diet may help in this respect.
One such study involved 10 obese people with diabetes. The study participants initially followed their normal diet for 7 days, then followed a very-low-carbohydrate diet (with about 20 grams of carbohydrate a day) for 14 days. Although the researchers didn’t restrict overall calorie intake, the effect of restricting carbohydrate intake spontaneously lowered participants’ calorie intake by about 1,000 calories per day. As a result of the 14-day dietary change, participants lost weight, lowered blood glucose levels, improved insulin sensitivity, and lowered triglyceride and cholesterol levels. However, it is unknown whether this diet could be continued over a longer term, whether its positive effects would continue, and what the effect of a greatly reduced fiber intake would be.
Adding exercise to diet
Regular exercise can improve diabetes control and heart disease risk and help with weight maintenance in many of the same ways that diet can. It can additionally build muscle (which burns more calories than fat) and increase strength and stamina.
To see what the effects would be of following a higher-protein diet while also following an exercise program, researchers in Illinois devised a study to find out. The study participants were 48 obese women and, as in the other studies described here, all consumed the same number of calories, but some consumed more protein and less carbohydrate, while others consumed less protein and more carbohydrate. In addition, some were educated about physical activity and encouraged to exercise voluntarily (this was the exercise control group), while others had a supervised exercise program that included aerobic activities and resistance training.
After 16 weeks, the researchers found that the women who ate more protein lost more total body weight and body fat than those who consumed more carbohydrate. However, the women in the supervised exercise group lost more body fat than those in the exercise control group, no matter which diet was followed.
The effects of a higher-protein diet and exercise were additive: The women in the higher-protein plus supervised exercise group experienced a 21.4% reduction of total body fat. In comparison, the women who followed the higher-carbohydrate diet and were in the exercise control group saw a 12.8% reduction in total body fat. In addition, the women in the higher-protein plus supervised exercise group were better able to maintain their levels of muscle tissue, while those in the higher-carbohydrate and exercise control groups lost almost 5% of their initial muscle mass.
Composing your own meal plan
Much debate continues over the ideal proportion of nutrients for people with diabetes, people trying to lose weight, and people facing both challenges. Luckily, scientific research is ongoing as well, so someday there may be real answers and not just the claims of popular diet books. It’s possible — even likely — that diet composition is not a one-size-fits-all proposition.
With that in mind, how should you make decisions about your own dietary makeup now? A good first step would be sitting down with a knowledgeable physician or dietitian to discuss your goals, your current eating habits, and any medical conditions you may have besides diabetes (such as kidney disease) that may affect what is safe and healthy for you to eat. You may also want to get out your calculator and a good nutrition resource to figure out what the proportions of carbohydrate, protein, and fat are in your current meal plan and what sort of changes you would need to make to alter them. And of course, you need to consider your overall calorie intake.
If you decide to increase the proportion of protein in your meal plan, it’s important to identify sources of protein that are low in saturated fat, such as skinless poultry, fish, soy products, nonfat or low-fat dairy products, and legumes. (A high intake of saturated fat can contribute to high LDL cholesterol.) In addition, talk to the members of your health-care team about how long to maintain your increased protein intake and how often to check in with your team to assess your health. (Click here to see two sample menus with varying degrees of macronutrients.)
If you cut the amount of carbohydrate you eat, it may be necessary to also cut back on the amount of blood-glucose-lowering medicines you currently use. This is also worth discussing with your physician.
No matter which way you cut it, losing weight requires burning more calories than you’re taking in. Research suggests, however, that — at least in the short term — having a higher percentage of protein and a lower percentage of carbohydrate in your diet may keep you from feeling overly hungry as you cut calories and may have additional benefits as well.