The Best Diet for Weight Loss Isn't the One You Think

By C. Erick Kaufman, MD — Medical Director, Holistically Rx

Every week a patient arrives at Holistically Rx loyal to a diet with a name — keto, low-fat, carnivore, intermittent fasting — and asks me which one is "the best." After decades of head-to-head research, medicine finally has a clear answer, and it surprises almost everyone: the best diet isn't a named diet at all.

The Trial That Settled the Argument

In the DIETFITS randomized trial, published in JAMA, 609 adults were assigned to a healthy low-fat or healthy low-carbohydrate diet for a full year. The result: a statistical dead heat. Average weight loss was essentially identical, and — here's the part that matters — neither genetics nor insulin levels predicted which diet would work better for whom.

What did predict success? Adherence. The people who lost the most weight, on either diet, were simply the ones who stuck with it. The composition of the diet mattered far less than the consistency of the person following it.

That's not a disappointing answer — it's a liberating one. If you've "failed keto" three times, you didn't fail dieting. You were on a plan you couldn't live with. The best diet is the one you'll still be following in two years.

The Pattern That Works

Consistency doesn't mean eating anything. Across the research, the eating pattern associated with better weight and health outcomes looks like this: reduce refined carbohydrates, processed meats, and trans fats; enjoy in moderation lean meats, eggs, and dairy; and build meals around vegetables, fruits, legumes, nuts, fish, minimally processed whole grains, and healthy oils like olive oil.

If that sounds like Mediterranean-style eating without the branding, that's exactly what it is — a flexible pattern rather than a rulebook, which is precisely why people can sustain it. It's the same philosophy behind building meals around fresh produce and the practical eating strategies we've shared before.

The One Food Category Worth Avoiding

If macronutrients don't deserve your vigilance, one category does: ultra-processed foods. In a landmark NIH inpatient trial, researchers fed people ultra-processed and unprocessed diets matched for calories, sugar, fat, and carbs available — and let them eat as much as they wanted. On the ultra-processed diet, people spontaneously ate about 500 more calories per day and steadily gained weight; on the unprocessed diet, the same people lost it. The food engineering itself — not just the nutrients — drives overeating.

The practical rule I give patients: shop mostly foods that don't have an ingredient list, and treat anything engineered to be irresistible as exactly that.

How Fast Should the Weight Come Off?

A sustainable target for lifestyle-driven weight loss is around a pound a week, which for most people means roughly a 500–750 calorie daily reduction — about 20% for many adults. Faster isn't automatically better: rapid loss raises the risk of losing muscle and bone along with fat, and is the classic setup for gallstones. (If you're losing faster on a GLP-1 medication, that can be appropriate — but it should be monitored, with the protein and resistance-training safeguards I covered in my article on protecting your muscle.)

Keeping It Off: What Actually Works

Maintenance has its own evidence base, and it rewards habits more than willpower: regular self-monitoring (weekly or better weigh-ins), sustained physical activity at higher volumes than most expect — on the order of 200–300 minutes weekly — and ongoing support rather than "graduating" from care. That last one is why our model at Holistically Rx is built on continuous follow-up, whether your plan is lifestyle alone or includes medication, as I discussed in my article on the new ACP obesity guidelines.

The Bottom Line

Stop searching for the perfect diet — it doesn't exist. Build a flexible, Mediterranean-style pattern you can genuinely live with, cut the ultra-processed foods that hijack your appetite, aim for a sustainable pace, and put your effort into consistency and support rather than rules. That's what the evidence rewards.

If you'd like help building an eating pattern that fits your life — with or without medical weight-loss support — schedule a free consultation with us at Holistically Rx.

This article is for educational purposes only and is not medical advice. Always consult your healthcare provider about your individual situation before making significant changes to your diet or starting or stopping any medication.