Weight-Loss Diets Compared: evidence, difficulty and cost

Key takeaways

• Healthy low-fat and healthy low-carb diets led to similar weight loss, about 5 to 6 kg, after 12 months in the DIETFITS trial.^[1]
• Across 121 trials, weight loss on every named diet shrank between 6 and 12 months: sticking with it matters more than the label.^[2]
• Whatever the diet, a healthy pattern has plenty of vegetables, fruits, whole grains and protein foods, with less added sugar, salt and saturated fat.^[3]
• A first goal of 5 to 10% of starting weight over about six months is a realistic target, according to the NIH.^[5]

In short: Many weight-loss diets work about equally well when people stick to them, because each one creates a calorie deficit in its own way. In large comparisons, low-carb and low-fat approaches led to similar weight loss, and most of the difference between named diets faded by one year. The best weight loss diet for you is the one that fits your tastes, budget, health and routine well enough to keep going.

This hub compares the popular diets side by side on evidence, effort, cost and how easy they are to maintain, then links to a full guide for each one. It is general information; if you have a health condition or take regular medication, check with your clinician or a registered dietitian before a big change in how you eat.

Start here: do these next 1-2-3

Diet scorecard: evidence, convenience, cost and maintenance

Each diet gets the same five ratings: how strong the evidence is, how much effort it takes, what it typically costs, how much upkeep it needs once you reach your goal, and whether medical supervision is recommended. There is no overall score, because the right trade-off is personal. Our comparison builder lets you put any two or three diets side by side.

No overall score. Commissions never change the order or the values.

All diets: filter by evidence, convenience and cost

What the research says about choosing a diet

Two big pieces of research shape how we compare diets:

• DIETFITS (JAMA, 2018). 609 adults followed either a healthy low-fat or a healthy low-carbohydrate diet for 12 months. Both groups lost a similar amount, about 5 to 6 kilograms (11 to 13 pounds) on average, and neither genetics nor insulin levels predicted who did better on which diet.
• A network meta-analysis in The BMJ (2020). Researchers pooled 121 randomized trials with nearly 22,000 adults and 14 named diets. At six months, low-carb and low-fat patterns produced similar weight loss compared with usual eating, about 4 to 5 kilograms. By 12 months, weight loss had shrunk for every pattern and named diet, and most improvements in heart risk factors had faded, with the Mediterranean diet as the main exception.

Healthy low-fat diet5.3 kg

Healthy low-carb diet6 kg

DIETFITS: average weight loss after 12 months

Item	Value
Healthy low-fat diet	5.3 kg
Healthy low-carb diet	6 kg

609 adults; the difference between the two diets was not statistically significant.

Source: Gardner et al., JAMA 2018 (DIETFITS trial) (checked on October 6, 2026)

Low-carb pattern4.6 kg

Low-fat pattern4.4 kg

BMJ 2020: weight loss at 6 months compared with usual eating

Item	Value
Low-carb pattern	4.6 kg
Low-fat pattern	4.4 kg

Approximate averages from a different set of studies than DIETFITS; by 12 months weight loss had shrunk for every pattern.

Source: Ge et al., BMJ 2020 (network meta-analysis of 121 trials) (checked on October 6, 2026)

The lesson is not that diets fail; it is that keeping going matters more than the label. That is why our scorecards rate convenience and maintenance next to evidence. The CDC describes a healthy eating plan for weight the same way regardless of the diet’s name: plenty of vegetables, fruits, whole grains, protein foods and healthy fats, with less added sugar, salt and saturated fat. Our nutrition hub covers those building blocks, and calorie deficit explains the energy math behind every diet.

The diets, by approach

Whole-food eating patterns. These focus on what to eat more of rather than strict rules, and suit people who want a long-term way of eating:

• Mediterranean diet: vegetables, legumes, whole grains, fish and olive oil; a 7-day starter is on its page.
• DASH diet: designed to lower blood pressure, with weight loss as a common bonus.
• Plant-based diet: mostly or entirely plants, from flexitarian to vegan.
• Paleo diet: unprocessed foods without grains, legumes or dairy, and its trade-offs.

Macronutrient-focused diets. These change the balance of carbs, fat and protein:

• High-protein diet: more protein to help with fullness and muscle while you lose weight.
• Low-carb diet: how low, what to eat and what the evidence shows.
• Keto diet: very low carb, its risks and who it suits.
• Carnivore diet: the claims, the limited evidence and the risks.

Timing and structure. These change when or how you eat more than what you eat:

• Intermittent fasting: 16:8, 5:2 and what the evidence shows compared with regular calorie cutting.
• Meal replacement shakes: structured, convenient and easy to count, if you can keep using them.

Prefer more support than a diet alone? Commercial programs such as WeightWatchers and Optavia package an eating plan with coaching or food. Our programs hub compares them.

What a diet can do beyond the scale

Weight is only one result. The CDC notes that losing even 5% of your body weight can improve blood pressure, cholesterol and blood sugar, and lower the risk of heart disease and type 2 diabetes. Diets differ in these extra effects. In the 2020 BMJ analysis, improvements in heart risk factors had mostly faded by 12 months for the named diets studied, while the Mediterranean diet still showed some benefit. If blood pressure is your main concern, the DASH diet was designed for it.

That is why each diet page lists its evidence beyond weight, the foods it emphasizes and limits, how much protein it provides, a typical weekly cost with its date, and a starter week. If you have diabetes, high blood pressure or high cholesterol, bring the numbers you track to your clinician so you can see whether a diet is helping more than the scale shows.

Diet, program or medication?

A diet is something you do on your own; a program adds coaching, structure or food; medical care can add medication or surgery for people who meet the criteria in the label or guideline. They are not either-or: every medical approach still includes eating changes. If you have tried diets on your own without the results you hoped for, that is common and not a failure. Medical weight loss explains what a clinician can add, and the comparison builder shows diets, programs and medications on the same scorecard.

How to choose: questions that matter more than the name

• Can I eat this way at family meals, at work and on weekends? A plan that only works on perfect days usually stops when life gets busy.
• Does it keep me full? Protein, fiber and whole foods tend to be more filling. In a tightly controlled NIH study, adults offered ultra-processed meals ate about 500 more calories a day than when offered unprocessed meals matched for nutrients.
• What does it cost? Some diets rely on specialty foods or shakes; others use ordinary groceries. The cost rating in the scorecard is a guide, and each diet page shows a typical weekly cost with its date.
• Is the pace realistic? The CDC notes that people who lose about 1 to 2 pounds a week are more likely to keep it off, and the NIH suggests a first goal of 5 to 10% of your starting weight over about six months.
• What happens after? Ask how you would eat once you reach your goal. Our keep it off hub covers that next stage.

Pairing a diet with movement helps too: see our exercise hub, especially strength training to keep muscle while you lose fat. To plan protein, try the protein calculator or the macro calculator.

Safety: who should check first

Changing how you eat is safe for most adults, but some people should talk with a clinician or registered dietitian before starting a restrictive plan:

• People who take medication for diabetes or blood pressure, since doses sometimes need adjusting when eating changes a lot.
• People with kidney, liver or heart disease, or a history of gallbladder problems.
• Anyone who is pregnant, breastfeeding or under 18.
• Anyone with a history of an eating disorder. In that case, the most helpful next step is support from a professional experienced in eating disorders, not a new diet.
• People taking a GLP-1 medication or after bariatric surgery, who have specific nutrition needs covered in what to eat on a GLP-1.

Each diet page has its own safety section listing who should check first and why. For a broader view of every option, from habits to medication, start at how to lose weight or try Find My Options.

Questions to ask a professional

• Is there any eating pattern I should avoid because of my health conditions or medications?
• Would any of my medications need adjusting if I cut carbs or calories a lot?
• How much protein and fiber should I aim for while losing weight?
• Would working with a registered dietitian help me, and is it covered by my insurance?
• Which lab tests or numbers should we check as I change my diet?

Frequently asked questions

What is the best diet for weight loss?

There is no single best diet for everyone. Large trials and reviews find similar results for many approaches when people stick with them, so the best choice is one that fits your food preferences, budget, health and routine.

Is low-carb better than low-fat for weight loss?

In the 12-month DIETFITS trial, healthy low-carb and healthy low-fat diets led to similar weight loss, and a 2020 analysis of 121 trials found the two patterns gave similar results at six months.

How fast should I lose weight on a diet?

The CDC links a pace of about 1 to 2 pounds a week with better long-term results, and the NIH suggests a first goal of 5 to 10% of your starting weight over about six months.

Why do people regain weight after a diet?

A smaller body uses less energy, and many diets are hard to keep up. Planning how you will eat after reaching your goal, staying active and keeping some tracking habits all help.

Do I need a dietitian to start a diet?

Many healthy adults can start on their own. People with diabetes, kidney, liver or heart disease, those taking regular medication, pregnant or breastfeeding people, and anyone with a history of an eating disorder should get professional advice first.

References

1. Gardner CD, Trepanowski JF, Del Gobbo LC, et al.. Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults (DIETFITS randomized clinical trial). JAMA, 2018. doi:10.1001/jama.2018.0245 · PMID 29466592 · NCT01826591 (accessed October 7, 2026) Randomized trial
2. Ge L, Sadeghirad B, Ball GDC, et al.. Comparison of dietary macronutrient patterns of 14 popular named dietary programmes for weight and cardiovascular risk factor reduction in adults: systematic review and network meta-analysis of randomised trials. BMJ, 2020. doi:10.1136/bmj.m696 · PMID 32238384 (accessed October 7, 2026) Meta-analysis
3. Healthy Eating for a Healthy Weight. Centers for Disease Control and Prevention. (accessed October 7, 2026) Government page
4. Steps for Losing Weight. Centers for Disease Control and Prevention. (accessed October 7, 2026) Government page
5. Choosing a Safe & Successful Weight-loss Program. National Institute of Diabetes and Digestive and Kidney Diseases (NIH). (accessed October 7, 2026) Government page
6. Hall KD, Ayuketah A, Brychta R, et al.. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metabolism, 2019. doi:10.1016/j.cmet.2019.05.008 · PMID 31105044 (accessed October 7, 2026) Randomized trial

Facts checked on October 6, 2026

Educational information, not medical advice. Talk with a qualified healthcare professional about your own situation. In an emergency call 911.