Low-Carb vs. Low-Fat Diets for Obesity

Overseen By Valerie L Darcey

Age: 18 - 65

Sex: Any

Trial Phase: Academic

Sponsor: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Must not be taking: Diet medications, Psychiatric medications

Disqualifiers: Diabetes, Cancer, Pregnancy, others

No Placebo Group All trial participants will receive the active study treatment (no placebo)

Compensation: Varies

Number of Visits: 5

42 Participants Needed

What You Need to Know Before You Apply

What is the purpose of this trial?

This trial tests how different diets affect weight loss in people with a BMI of 25 or more, indicating overweight or obesity. Researchers compare the effects of starting with a low-fat diet (also known as a plant-based or high-carbohydrate diet) followed by a low-carb diet (also known as a ketogenic or low-carbohydrate diet) to starting with a low-carb diet followed by a low-fat diet, each for four weeks. Participants will receive all their meals at home and track their weight and physical activity. This study suits individuals who are overweight or obese, have stable weight, and can follow a set diet plan at home. As an unphased trial, it offers a unique opportunity to explore personalized diet strategies for effective weight management.

Will I have to stop taking my current medications?

The trial requires that participants do not take prescription medications or other drugs that may influence metabolism, so you may need to stop taking certain medications if they affect your metabolism.

Is there any evidence suggesting that this trial's treatments are likely to be safe?

Research shows that both low-carb and low-fat diets can be safe for adults who are overweight or obese. Studies have found that people on a low-carb diet for a month or more can lose weight effectively without major safety issues. Most individuals handle these diets well, though some might experience minor issues like headaches or tiredness initially.

Low-fat diets have also been extensively studied and are considered safe for weight loss. These diets can aid in weight loss and improve the body's sugar metabolism.

Overall, both diets are generally well-tolerated and can be safe options for managing weight in adults who are overweight or obese. However, individual experiences may vary, so monitoring the body's response is important. ^{1 2 3 4 5}

Why are researchers excited about this trial?

Researchers are excited about this trial because it explores how different diet strategies can impact obesity. Unlike traditional treatments that often involve medication or surgery, this trial looks at the effects of dietary changes alone—specifically, a low-fat diet and a low-carbohydrate diet. Each diet is followed for four weeks, allowing researchers to directly compare their effectiveness and see which approach might be more beneficial for weight loss and health improvement. This trial could offer valuable insights into non-invasive, lifestyle-based strategies for managing obesity, potentially making it easier for people to adopt healthier habits without the need for more intense interventions.

What evidence suggests that this trial's treatments could be effective for obesity?

This trial will compare the effects of low-carbohydrate and low-fat diets on weight loss and health in adults with overweight or obesity. Research has shown that low-carbohydrate diets can help people with obesity lose weight and improve their health. Studies have found that these diets can lead to more weight loss and better control of conditions like type 2 diabetes. People on a low-carbohydrate diet often see a decrease in body fat and improvements in overall health.

Similarly, low-fat diets can also aid in weight loss. Research indicates that these diets can reduce body fat and improve insulin function, which controls blood sugar. One study comparing low-fat and low-carbohydrate diets found both effective, but the best choice may depend on personal preferences and adherence. Both diet types offer benefits, and their effectiveness can vary from person to person. Participants in this trial will experience both diets, with one group starting with a low-fat diet followed by a low-carbohydrate diet, and the other group starting with a low-carbohydrate diet followed by a low-fat diet. ^{1 2 4 6 7}

Who Is on the Research Team?

Valerie L Darcey

Principal Investigator

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Are You a Good Fit for This Trial?

This trial is for adults aged 19 to 50 with a BMI of 25 or higher. Participants will follow and switch between low-fat and low-carb diets over an 8-week period, all while living at home. They must be willing to visit the NIH three times, track their weight daily, monitor physical activity and glucose levels, and attend virtual meetings.

Inclusion Criteria

Stated willingness to comply with all study procedures and availability for the duration of the study

Weight stable (< +/- 5 % over past 6 months) as determined by volunteer report

Body mass index (BMI) >= 25 kg/m2

Exclusion Criteria

Positive pregnancy test or lactating as determined by volunteer report (women only)

Inadequate access to equipment required for the study (e.g., too little refrigerator storage space or a microwave oven that is too small) as determined by discretion of PI and/or study team

Regular vigorous exercise >150 min per week as determined by volunteer report

Timeline for a Trial Participant

Screening

Participants are screened for eligibility to participate in the trial

2 weeks

1 visit (in-person)

Baseline Testing

Participants undergo baseline testing including metabolism tests, scans for bone density, and collection of stool, blood, and urine samples

1 day

1 visit (in-person)

Diet Phase 1

Participants follow a specific diet (either low-fat or low-carbohydrate) for 4 weeks with meals delivered to their homes

4 weeks

1 visit (in-person), weekly virtual meetings

Diet Phase 2

Participants switch to the alternate diet (low-carbohydrate or low-fat) for another 4 weeks with meals delivered to their homes

4 weeks

1 visit (in-person), weekly virtual meetings

Follow-up

Participants are monitored for changes in body weight and fat mass, with final measurements taken

2 weeks

1 visit (in-person)

What Are the Treatments Tested in This Trial?

Interventions

• Low-carbohydrate Diet
• Low-fat Diet

Trial Overview The study tests whether starting with a low-carbohydrate diet leads to greater body fat loss compared to starting with a low-fat diet when each is followed for four weeks at home. Meals are provided, and participants' metabolism, bone density, muscle mass, body fat, and various health markers are monitored.

How Is the Trial Designed?

Group I: low-fat diet then low-carbohydrate diet Experimental Treatment 2 Interventions

A low-fat followed by low-carbohydrate diet, each lasting for 4 weeks in adults with overweight or obesity

Group II: low-carbohydrate diet then low-fat diet Experimental Treatment 2 Interventions

A low-carbohydrate followed by low-fat diet, each lasting for 4 weeks in adults with overweight or obesity

Who Is Running the Clinical Trial?

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Lead Sponsor

Trials

2,513

Recruited

4,366,000+

Published Research Related to This Trial

In a study of 82,802 women over 20 years, low-carbohydrate diets were not linked to an increased risk of coronary heart disease, suggesting they can be safe for long-term use.

Diets that emphasize vegetable sources of fat and protein, while being lower in carbohydrates, may even reduce the risk of coronary heart disease, highlighting the importance of food sources in dietary choices.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Low-carbohydrate-diet score and the risk of coronary heart disease in women. Halton, TL., Willett, WC., Liu, S., et al.[2022]

There is no evidence that increased fat intake is responsible for the rise in obesity, and diets with 30-35% of energy from fat can actually promote weight loss.

High-carbohydrate diets, especially those with a high glycaemic index, can lead to insulin resistance, but this can be countered by increased physical activity, highlighting the importance of exercise in managing diet-related health issues.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

High- versus low-fat diets in human diseases. Sanders, TA.[2019]

Low-carbohydrate diets lead to greater short-term weight loss compared to low-fat diets for overweight or obese individuals, particularly within the first 6 months.

There is currently a lack of research on the long-term safety and efficacy of both low-fat and low-carbohydrate diets for sustained weight management.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Clinical trial experience with fat-restricted vs. carbohydrate-restricted weight-loss diets. Klein, S.[2007]

Low-fat, high-complex carbohydrate diets can effectively promote weight loss in obese individuals, with a reduction of 10% in dietary fat leading to an average weight loss of about 5 kg, especially in those who adhere to the diet.

After significant weight loss, following an ad libitum low-fat diet is more effective for maintaining weight loss over two years compared to traditional caloric counting methods.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

The role of low-fat diets and fat substitutes in body weight management: what have we learned from clinical studies? Astrup, A., Toubro, S., Raben, A., et al.[2019]

Meta-analyses of low-fat diets show significant weight loss (3-4 kg) in normal-weight and overweight individuals, indicating that reducing dietary fat is effective for weight management.

Replacing carbohydrates with protein in a low-fat diet can lead to greater weight loss, suggesting that protein is more satiating and beneficial for weight control compared to high-monounsaturated fat diets.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Low-fat diets and energy balance: how does the evidence stand in 2002? Astrup, A., Astrup, A., Buemann, B., et al.[2006]

Low-fat diets in obese patients result in modest weight loss of 3-4 kg over 3 years, while calorie-controlled diets show better outcomes with 6-7 kg weight loss at 4 years, although long-term data is limited.

Bariatric surgery, such as gastric bypass, can lead to significant weight loss (up to 25% over 10 years) and reduce mortality and comorbidities, but it carries risks of nutritional deficiencies and gastrointestinal issues.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Dietary treatment for obesity. Clifton, PM.[2022]

Low-carbohydrate/high-protein diets were found to be more effective than low-fat/high-carbohydrate diets for weight loss and improving cardiovascular risk factors, based on a systematic review of 13 randomized controlled trials lasting at least 6 months.

Participants showed a preference for low-carbohydrate diets, as indicated by a higher dropout rate in the low-fat diet group, suggesting that these diets may be more sustainable for long-term weight management.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Systematic review of randomized controlled trials of low-carbohydrate vs. low-fat/low-calorie diets in the management of obesity and its comorbidities. Hession, M., Rolland, C., Kulkarni, U., et al.[2022]

In a study of 200 obese adults over six months, the low-carbohydrate ketogenic diet (LCKD) resulted in a significant weight loss of 13.0 kg compared to 4.7 kg with the low-caloric fat low diet (LCLF), indicating that LCKD is more effective for weight reduction.

The LCKD also led to greater reductions in fat mass and visceral fat, while not increasing cholesterol or uric acid levels, suggesting it is a safe and effective option for obesity management.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

The effect of low-carbohydrate ketogenic diet in the management of obesity compared with low caloric, low-fat diet. Al Aamri, KS., Alrawahi, AH., Al Busaidi, N., et al.[2022]

Low-carbohydrate diets can lead to greater initial weight loss (3-6 kg) compared to conventional low-fat diets, particularly noticeable at 6 months, but this difference diminishes after 12 months.

While low-carb diets do not increase LDL cholesterol and can improve HDL cholesterol and lower triglycerides, they may pose long-term health risks due to low intake of essential nutrients and fiber, making them unsuitable for general recommendation.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

[Low-carbohydrate diets for obesity]. Keller, U., Rastalsky, N.[2008]

In a 12-week study involving 55 obese participants, a high fat, low carbohydrate (HFLC) diet led to greater improvements in blood lipids and inflammation markers compared to a low fat, high carbohydrate (LFHC) diet, despite similar changes in body weight and composition.

The HFLC group experienced significant increases in HDL cholesterol and total adiponectin, along with decreases in serum triglycerides and hs-CRP, suggesting potential cardiovascular benefits from this dietary approach.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Consuming a hypocaloric high fat low carbohydrate diet for 12 weeks lowers C-reactive protein, and raises serum adiponectin and high density lipoprotein-cholesterol in obese subjects. Ruth, MR., Port, AM., Shah, M., et al.[2022]

Low-carbohydrate diets (LCDs) significantly reduced HbA1c levels by 0.35% and led to greater body weight loss compared to low-fat diets (LFDs) in type 2 diabetes patients, based on a review of 12 randomized controlled trials involving 761 participants.

LCDs also improved cardiovascular risk factors by lowering triglycerides and increasing HDL cholesterol, with these benefits lasting up to 2 years, although the weight loss effects diminished after 2 years.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Comparing the Efficacy and Safety of Low-Carbohydrate Diets with Low-Fat Diets for Type 2 Diabetes Mellitus Patients: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Li, S., Ding, L., Xiao, X.[2022]

Citations

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Effect of carbohydrate restriction on body weight in ... Carbohydrate restriction is an effective dietary strategy for important weight loss in adults with overweight and obesity.