The findings of the largest-ever clinical trial contradict the weight-control advice advocated in the USDA Food Guide Pyramid.
The USDA and other public health authorities worldwide tend to recommend higher-carb, lower-protein, lower fat diets as ideal for weight control.
But the Danish researchers who led an unprecedented clinical trial found the best weight control effects from lower-carb diets that got ample protein ... mostly from veggies, fish, beans, low-fat dairy, and lean meats.
And they described what their data suggests is the best kind of higher-protein, lower-carb diet: "Eat fruit, vegetables and fish and go easy on the fat” (UC 2010).
World's largest diet trial finds that higher-protein, lower-carb diets work best
Researchers from the University of Copenhagen studied the effects of various diets in 772 families participating in the European Diogenes diet study, which included 938 overweight adults and their 827 children, almost half of who were overweight.
This was the largest controlled clinical trial testing weight control diets ever conducted.
The objective was to compare the official dietary recommendations in Europe—which resemble the advice depicted in the USDA’s Food Guide Pyramid—with a diet based on the latest knowledge about the various impacts of proteins and carbohydrates on appetite regulation.
Five diet types tested
The 938 overweight adults initially consumed only 800 calories per day for eight weeks, and lost an average of 24 lbs. (11 kg).
Such a very-low calorie diet is unsustainable, but it reduce the volunteers’ weight enough so that the scientists could test the relative success (or failure) of various diets in preventing weight regain.
After eight weeks of extreme calorie restriction, the volunteers were randomly assigned to one of five different low-fat diet types for six months.
Throughout the project, the families received expert guidance from dieticians and were asked to provide blood and urine samples.
The five different diet types were characterized by different protein contents and differences in their overall "glycemic index” (GI), which is a measure of how much various carbohydrate-containing foods increase blood sugar (glucose) levels.
Carbohydrate-containing foods with a low glycemic index (e.g., beans, green vegetables, nuts, some whole grains) cause blood glucose levels to increase more slowly and to lower levels, compared to high-carbohydrate foods with high glycemic indices, such as sugars, refined grains, fruit juices, and sugar-sweetened sodas.
The trial tested five diets:
Low-protein (13% of calories)/high-GI diet
High-protein (25% of calories)/low-GI diet
A control group followed the current, USDA-like European dietary recommendations
And the outcomes favored diet number three... the high-protein (25% of calories)/low-GI diet.
High-protein, low-GI diet worked best
Of the 938 adult participants, 548 completed both the initial weight-loss phase and the subsequent six-month diet intervention where they were assigned to different diet types.
The average weight regain among the participants was just over one pound (0.5 kg) but there were significant differences among the diets.
The people in the high-protein/low-GI diet group were the only ones who maintained their weight loss after the initial 24 lb. (11 kg) drop.
In comparison, those in the low-protein/high-GI group showed a weight gain of 3.6 lbs. (1.67 kg).
The researchers also noted that fewer participants in the high-protein/low-GI group dropped out of the trial, compared with the low-protein, high-GI group.
As lead author Thomas Meinert Larsen explained, this advantage may be due to a low-GI diet resulting in slower digestion and preventing the kinds of blood sugar swings that lead to carb cravings.
Also, said Dr. Larsen, proteins satisfy appetites more than carbohydrates and fat can.
Overweight children lose weight without going on a diet
About 45 percent of the 827 children in these volunteer families were overweight.
They ate normally while their parents were on the low-calorie weight loss diet for eight weeks.
But when their parents began to eat their assigned test diets, the children followed suit, with results similar to those seen in their parents:
And in the high-protein/low-GI diet, the number of overweight children dropped by about 15 percent in six months.
As Professor Arne Astrup said in a press release, "This is remarkable because the children were not on a slimming diet or counting calories. The families just changed their diet. This gives hope that we can prevent child obesity by just making the children eat a slightly different diet.”
Raw and cold foods found helpful
When it comes to standard recommendations to eat plenty of fruit and vegetables and fiber, and to limit sugar intake, the new research results fit with official dietary recommendations.
But the Danes called this approach insufficient to lose weight or maintain weight loss: "… according to our study, some fruits can be eaten freely whereas the intake of others should be limited. And vegetables such as carrots, beets and parsnip should preferably be eaten raw…” (UC 2010).
As Dr. Larsen noted, the starches in potatoes, corn, and pasta convert to so-called "resistant starches” when they are rapidly cooled (See "Beans Seen to Discourage Weight Gain and Diabetes” and look for the section titled "Grains and resistant starch: Making a good thing better” midway down the article).
As he noted, "…[resistant starches] are broken down more slowly in the intestines, which ensures more stable blood glucose levels” (UC 2010).
Cook pasta al dente and rinse it in cold water… better yet, do that and then eat it cold in salads.
Likewise, salads featuring minimally cooked, rapidly cooled potatoes, grains, or corn are less glycemic than hot grains, corn, or potatoes.
Bladbjerg EM, Larsen TM, Due A, Jespersen J, Stender S, Astrup A. Long-term effects on haemostatic variables of three ad libitum diets differing in type and amount of fat and carbohydrate: a 6-month randomised study in obese individuals. Br J Nutr. 2010 Jul 30:1-7. [Epub ahead of print]
Larsen TM, Dalskov SM, van Baak M, Jebb SA, Papadaki A, Pfeiffer AF, Martinez JA, Handjieva-Darlenska T, Kunešová M, Pihlsgård M, Stender S, Holst C, Saris WH, Astrup A; Diet, Obesity, and Genes (Diogenes) Project. Diets with high or low protein content and glycemic index for weight-loss maintenance. N Engl J Med. 2010 Nov 25;363(22):2102-13.
Papadaki A, Linardakis M, Larsen TM, van Baak MA, Lindroos AK, Pfeiffer AF, Martinez JA, Handjieva-Darlenska T, Kunesová M, Holst C, Astrup A, Saris WH, Kafatos A; DiOGenes Study Group. The effect of protein and glycemic index on children's body composition: the DiOGenes randomized study. Pediatrics. 2010 Nov;126(5):e1143-52. Epub 2010 Oct 11.
University of Copenhagen (UC). Dietary recommendations no cure for obesity. Nov. 11, 2010. Accessed at http://news.ku.dk/all_news/2010/2010.11/diogens/