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Diet (weight loss)

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Diets may be used in the treatment of obesity.

Descriptions of common diets

Descriptions of common diets
Diet Description
American Heart Association diet[1] low fat
Dr Atkins' diet Carbohydrate-restricted
initially < 20 g of carbohydrate daily, subsequently 50 g/day
LEARN diet low fat
Mediterranean diet[2] moderate-fat (<35% of calories) emphasizing monounsaturated fats
Ornish diet vegetarian, low fat
Rosemary Conley low-fat and social support
Slim-Fast plan low glycemic index
SouthBeach diet plan Carbohydrate-restricted; meal replacement
Weight Watchers balanced diet with social support
Zone diet low-carbohydrate diet
carbohydrates, proteins, and fats in 40:30:30 ratio

The United States Department of Health and Human Services and Department of Agriculture jointly recommend:[3]

  • "Keep total fat intake between 20 to 35 percent of calories."
    • "Consume less than 10 percent of calories from saturated fatty acids"
    • "Less than 300 mg/day of cholesterol"
    • "Keep trans fatty acid consumption as low as possible"
  • "The Average Macronutrient Distribution Range (AMDR) for carbohydrates is 45 to 65 percent of total calories."
    • "The recommended dietary fiber intake is 14 grams per 1,000 calories consumed." offer online dietary support at

Evidence for effectiveness

In a meta-analysis of 11 randomized controlled trials that compared low fat versus low carbohydrate diets, low fat diets achieved greater reduction in low density lipoprotein but less weight loss and less increase in high density lipoprotein.[4]

Major randomized controlled trials of commercial weight loss programs with outcomes at one year* using BOCF†[5] [6] [7] [8] [9] [10]
Study Intervention Results (kg) Comments
Intervention Control
Heshka et al[5]
Weight Watchers 4.3 1.3  
Dansinger et al[6]
Weight Watchers
3.0 NA
(no control group)
A to Z Weight Loss Study
Gardner et al[7]
• 2 months
4.7 2.2
Rock et al[8]
Jenny Craig plus center-based counseling 10.1 2.4 7.4 kg in intervention group after two years
Lighten Up
Jolly et al[9]
Weight Watchers
• 3 months
3.5 2.0  
Jebb et al[10]
Weight Watchers
• 12 months
4.1 1.8  
* Excluded BBC diet trials which only lasted six months.[11] However, BBC noted, "higher discontinuation rates for the Atkins and Ornish diet groups."
BOCF. Baseline observation carried forward.
Randomized controlled trials by the Practice-based Opportunities for Weight Reduction (POWER) Trials Collaborative Research Group. Results at two years using BOCF†.[12] [13] [14]
Study Intervention Results at two years (kg) Comments
Intervention Control
Appel et al[13]
In person support: 5.1
Remote support: 4.6
Wadden et al[14]
Brief Lifestyle Counseling plus either meal replacements or weight loss medication (enhanced) Enhanced Brief Lifestyle Counseling: 4.6
Brief Lifestyle Counseling: 2.9
The Be Fit, Be Well (BFBW)
Colditz et al
NCT00661817 Not published
Lifestyle Modification Program      
* BOCF. Baseline observation carried forward.

Various alternative dietary approaches have been proposed, some of which have been compared by randomized controlled trials:

  • A comparison of varying fat and protein levels found no difference on weight loss.[15] The lowest-carbohydrate group had a slightly better improvement in the HDL.

Carbohydrate-restricted (low carbohydrate) versus fat-restricted (low fat) diets

Many studies have focused on diets that reduce calories via a low-carbohydrate (Atkins diet, South Beach diet, Zone diet) diet (< 20-30 grams/day of carbohydrate) versus a low-fat diet (LEARN diet, Ornish diet). The Nurses' Health Study, an observational cohort study, found that low carbohydrate diets based on vegetable sources of fat and protein are associated with less coronary heart disease.[16]

A comparison of three diets: 1) low-fat, restricted-calorie; 2) Mediterranean, restricted-calorie; or 3) low-carbohydrate, non-restricted-calorie found:[17]

  • Least weight loss occurred in the low-fat, restricted-calorie group
  • More favorable effects on lipids with the low-carbohydrate diet
  • More favorable effects on glycemic control with the Mediterranean diet

A meta-analysis that included older randomized controlled trials[18][19][6] (but not the two more recent studies above) found:[20]

"low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered."

An older meta-analysis of randomized controlled trials by the Cochrane Collaboration in 2002 concluded[21] that fat-restricted diets are no better than calorie restricted diets in achieving long term weight loss in overweight or obese people.

The Women's Health Initiative Randomized Controlled Dietary Modification Trial[22] found that a diet of total fat to 20% of energy and increasing consumption of vegetables and fruit to at least 5 servings daily and grains to at least 6 servings daily:

  • no reduction in cardiovascular disease[23]
  • an insignificant reduction in invasive breast cancer[24]
  • no reductions in colorectal cancer[25]

In other randomized controlled trials, a comparison of Atkins, Zone diet, Ornish diet, and LEARN diet in premenopausal women found the greatest benefit from the Atkins diet.[7]

The choice of diet for a specific person may be influenced by measuring the individual's insulin secretion:

In young adults "Reducing glycemic [carbohydrate] load may be especially important to achieve weight loss among individuals with high insulin secretion."[26] This is consistent with prior studies of diabetic patients in which low carbohydrate diets were more beneficial.[27][28]

Low glycemic index and low glycemic load diets

For more information, see: glycemic index.

A meta-analysis by the Cochrane Collaboration concluded that low glycemic index or low glycemic load diets led to more weight loss and better lipid profiles. However, the Cochrane Collaboration grouped low glycemic index and low glycemic load diets together and did not try to separate the effects of the load versus the index.[29]

A randomized controlled trial that compared four diets that varied in carbohydrate amount and glycemic index found complicated results[30]:

  • Diet 1 and 2 were high carbohydrate (55% of total energy intake)
    • Diet 1 was high-glycemic index
    • Diet 2 was low-glycemic index
  • Diet 3 and 4 were high protein (25% of total energy intake)
    • Diet 3 was high-glycemic index
    • Diet 4 was low-glycemic index

Diets 2 and 3 lost the most weight and fat mass; however, low density lipoprotein fell in Diet 2 and rose in Diet 3. Thus the authors concluded that the high-carbohydrate, low-glycemic index diet was the most favorable.

High versus standard protein

There was no difference from amount of protein according to a randomized controlled trial.[31]


  1. Krauss RM, Eckel RH, Howard B, et al (October 2000). "AHA Dietary Guidelines: revision 2000: A statement for healthcare professionals from the Nutrition Committee of the American Heart Association". Circulation 102 (18): 2284–99. PMID 11056107[e]
  2. (2005) Eat, Drink, and Be Healthy : The Harvard Medical School Guide to Healthy Eating. New York: Free Press. LCC RA784 .W635. ISBN 0-7432-6642-0. 
  3. Key Recommendations for the General Population, Dietary Guidelines for Americans 2005. United States Department of Agriculture (2005). Retrieved on 2008-07-01.
  4. Mansoor N, Vinknes KJ, Veierød MB, Retterstøl K (2016). "Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials.". Br J Nutr 115 (3): 466-79. DOI:10.1017/S0007114515004699. PMID 26768850. Research Blogging.
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  8. 8.0 8.1 Rock CL, Flatt SW, Sherwood NE, Karanja N, Pakiz B, Thomson CA (2010). "Effect of a free prepared meal and incentivized weight loss program on weight loss and weight loss maintenance in obese and overweight women: a randomized controlled trial.". JAMA 304 (16): 1803-10. DOI:10.1001/jama.2010.1503. PMID 20935338. Research Blogging.
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  13. 13.0 13.1 Appel LJ, Clark JM, Yeh HC, Wang NY, Coughlin JW, Daumit G et al. (2011). "Comparative Effectiveness of Weight-Loss Interventions in Clinical Practice.". N Engl J Med. DOI:10.1056/NEJMoa1108660. PMID 22085317. Research Blogging.
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