- Dietary guidelines have changed over the years as research becomes more accurate in determining what we should eat to attain optimal health and weight. The strongest evidence to date shows that calories matter, but focusing on food quality is an equally important part of preventing weight gain and promoting weight loss.
- Focus on eating high-quality foods in appropriately sized portions.
Consider quality, not just calories
“A calorie is a calorie” is an oft-repeated dietary slogan, and not overeating is indeed an important health measure. Rather than focusing on calories alone, however, emerging research shows that quality is also key in determining what we should eat and what we should avoid in order to achieve and maintain a healthy weight. Rather than choosing foods based only on caloric value, think instead about choosing high-quality, healthy foods, and minimizing low-quality foods.
- High-quality foods include unrefined, minimally processed foods such as vegetables and fruits, whole grains, healthy fats and healthy sources of protein – the foods recommended in the Healthy Eating Plate.
- Lower-quality foods include highly processed snack foods, sugar-sweetened beverages, refined (white) grains, refined sugar, fried foods, foods high in saturated and trans fats, and high-glycemic foods such as potatoes.
There isn’t one “perfect” diet for everyone, owing to individual differences in genes and lifestyle.
One study analyzed whether certain foods were more or less likely to promote weight gain. This type of research examining specific foods and drinks allows us to understand whether “a calorie is a calorie,” or if eating more higher-quality foods and fewer lower-quality foods can lead to weight loss and maintenance.
Researchers in the Department of Nutrition at Harvard School of Public Health show us that quality is in fact very important in determining what we should eat to achieve and maintain a healthy weight, and that the notion of “a calorie is a calorie” does not tell the whole story.
- In a study of over 120,000 healthy women and men spanning 20 years, researchers determined that weight change was most strongly associated with the intake of potato chips, potatoes, sugar-sweetened beverages, and both processed and unprocessed red meats. The researchers concluded that consumption of processed foods higher in starches, refined grains, fats, and sugars can increase weight gain.
- Foods shown to be associated with weight loss were vegetables, whole grains, fruits, nuts, and yogurt.
- Researchers did not discount the importance of calories, instead suggesting that choosing high-quality foods (and decreasing consumption of lower-quality foods) is an important factor in helping individuals consume fewer calories. (23)
View the HSPH news release, “Changes in specific dietary factors may have big impact on long-term weight gain: Weight-loss Strategy to Only ‘Eat Less, Exercise More” May be Overly Simplistic’”
Managing macronutrients: Does it matter?
With the proliferation of macronutrient-based diets over the past several decades, from low-fat to low-carbohydrate, discussion of the three main macronutrients – carbohydrates, proteins, and fats – has become standard when talking about optimal diets. Researchers have begun comparing these “macronutrient management”-style diets to one another in order to determine which is most effective, but thus far evidence is largely inconclusive.
One study, published in JAMA in 2007, compared four weight-loss diets ranging from low to high carbohydrate intake. This 12-month trial followed over 300 overweight and obese premenopausal women, randomly assigning them to either an Atkins (very low carbohydrate), Zone (low carbohydrate), LEARN (high carbohydrate), or Ornish (very high in carbohydrate) diet.
- After one year, weight loss was greater for women in the Atkins diet group compared with the other diet groups.
- This study also examined secondary outcomes focused on metabolic effects (such as cholesterol, body fat percentage, glucose levels and blood pressure), and found that those for the Atkins group were comparable with or more favorable than the other diet groups.
- There was no significant difference in weight loss among the other three diets (Zone, LEARN, and Ornish).
- This study does raise questions about about long-term effects and mechanisms, but the researchers concluded that a low-carbohydrate, high-protein, high-fat diet may be considered a feasible recommendation for weight loss. (24)
Another study, published in The New England Journal of Medicine in 2009, challenged the above study’s findings by testing four different types of diets and producing results that showed comparable average weight loss among the different diets.
- The study followed 800 people over 2 years, assigning subjects to one of four diets: Low-fat and average-protein, low-fat and high-protein, high-fat and average-protein, and high-fat and high protein.
- Researchers concluded that all of the diets resulted in meaningful weight loss, despite the differences in macronutrient composition.
- The study also found that the more group counseling sessions participants attended, the more weight they lost, and the less weight they regained. This supports the idea that not only is what you eat important, but behavioral, psychological, and social factors are important for weight loss as well. (25)
An additional study, published in The New England Journal of Medicine in 2010, looked at the role of protein and glycemic index upon weight loss maintenance. Researchers first implemented a low-calorie diet to produce weight loss, then examined whether protein and glycemic index impacted weight loss maintenance.
- The study population was made up of nearly 800 overweight adults from European countries who had lost at least 8% of their initial body weight with a low-calorie diet. Participants were then assigned one of five diets to prevent weight regain over a 26-week period: A low-protein and low-glycemic-index diet, a low-protein and high-glycemic-index diet, a high-protein and low-glycemic-index diet, a high-protein and high-glycemic-index diet, or a control diet.
- The low-protein-high-glycemic-index diet was associated with subsequent significant weight regain, and weight regain was less in the groups assigned to a high-protein diet than in those assigned to a low-protein diet, as well as less in the groups assigned to a low-glycemic-index diet than in those assigned to a high-glycemic-index diet.
- These results show that a modest increase in protein content and a modest reduction in the glycemic index led to an improvement in maintenance of weight loss. (26)
The results from these three studies suggest that there may be some benefits to a macronutrient-based dietary approach, but research also shows that while a particular diet may result in weight loss for one person, it may not be effective for another person due to individual differences in genes and lifestyle. For those seeking the “perfect” one-size-fits-all diet, then, there isn’t one! The great news is that everyone can follow The Healthy Eating Plate guidelines and choose healthy, flavorful foods to create a diet that works best for you.
23. Mozaffarian, D., et al., Changes in diet and lifestyle and long-term weight gain in women and men. N Engl J Med, 2011. 364(25): p. 2392-404.
24. Gardner, C.D., et al., Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA, 2007. 297(9): p. 969-77.
25. Sacks, F.M., et al., Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med, 2009. 360(9): p. 859-73.
26. Larsen, T.M., et al., Diets with high or low protein content and glycemic index for weight-loss maintenance. N Engl J Med, 2010. 363(22): p. 2102-13.
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