Which diet is best for long-term weight loss?

Much has been made of the recently published results of the DIETFITS (Diet Intervention Examining the Factors Interacting with Treatment Success) study. Most of the headlines emphasized the fact that the two diets involved — low-fat and low-carb — ended up having the same results across almost all end points studied, from weight loss to lowering blood sugar and cholesterol.

What’s most interesting, however, is how these two diets are similar.

The authors wanted to compare low-fat vs. low-carb diets, but they also wanted to study genetic and physical makeups that purportedly (their word) could influence how effective each type of diet will be for people. Previous studies had suggested that a difference in a particular genetic sequence could mean that certain people will do better with a low-fat diet. Other studies had suggested that insulin sensitivity may mean that certain people will do better with a low-carb diet.

What DIETFITS revealed about weight loss

The study began with 609 relatively healthy overweight and obese people, and 481 completed the whole year. For the first month, everyone did what they usually did. Then, for the next eight weeks, the low-fat group reduced their total fat intake to 20 grams per day, and the low-carb group reduced their total carbohydrate intake to 20 grams per day. These are incredibly restricted amounts, considering that there are 26 grams of carbs in the yogurt drink I’m enjoying as I write this, and 21 grams of fat in my half of the dark chocolate bar my husband and I split for dessert last night.

That kind of dietary restriction is impossible to maintain over the long term and, as this study showed, unnecessary. Participants were instructed to slowly add back fats or carbs until they reached a level they felt could be maintained for life. In addition, both groups were instructed to

People were not asked to count calories at all. Over the course of a year, both groups attended 22 classes reinforcing these very sound principles — and all participants had access to health educators who guided them in behavioral modification strategies, such as emotional awareness, setting goals, developing self-efficacy (also known as willpower), and utilizing social support networks, all to avoid falling back into unhealthy eating patterns.

Participants in both groups also were encouraged to maintain current US government physical activity recommendations, which are “150 minutes of moderate intensity aerobic physical activity (2 hours and 30 minutes) each week.”

Two different diets that are not so different after all

Get all that? Basically, the differences between groups were minimal. Yes, the low-fat group dropped their daily fat intake and the low-carb group dropped their daily carb intake. But both groups ended up taking in 500 to 600 calories less per day than they had before, and both lost the same average amount of weight (12 pounds) over the course of a year. Those genetic and physical makeups didn’t result in any differences either. The only measure that was different was that the LDL (low density lipoprotein) was significantly lower in the low-fat group, and the HDL (high density lipoprotein) was significantly higher in the low-carb group.

I love this study because it examined a realistic lifestyle change rather than just a fad diet. Both groups, after all, were labeled as healthy diets, and they were, because study investigators encouraged eating high-quality, nutritious whole foods, unlimited vegetables, and avoiding flours, sugars, bad fats, and processed foods. Everyone was encouraged to be physically active at a level most Americans are not. And — this is a big one — everyone had access to basic behavioral counseling aimed at reducing emotional eating.

When it comes to diet, everything old is new again

This whole study could just as well be called a study of sustainable healthy lifestyle change. The results jibe very much with prior research about healthy lifestyle. The end message is the same one that we usually end with:

The best diet is the one we can maintain for life and is only one piece of a healthy lifestyle. People should aim to eat high-quality, nutritious whole foods, mostly plants (fruits and veggies), and avoid flours, sugars, trans fats, and processed foods (anything in a box). Everyone should try to be physically active, aiming for about two and a half hours of vigorous activity per week. For many people, a healthy lifestyle also means better stress management, and perhaps even therapy to address emotional issues that can lead to unhealthy eating patterns.

Image: vadimguzhva-iStock

Related Information: Lose Weight and Keep It Off


  1. carina

    All the recipes you’ll ever need to live and eat well on the ketogenic diet! i was overweight,
    exhausted, moody, and suffering from a range of physical discomforts when i found the ketogenic diet.
    But all that changed once i adopted its high fat, low carb principles. You too can reap the benefits of the
    ketogenic diet with Bacon & Butter, my ultimate companion for keto cooking, today and every day. its free if you want to review it

  2. Martin

    The best way to long term weight loss is a good meal plan and workout every single day ! this message is just to wish you courage in your change and achievement of your goals, you deserve to feel better in your body

  3. Laura Pagee

    One year is not “long term.” Research has demonstrated that, five years post-fad diet, almost everyone regains almost all, or even more, than the weight they started at when they started their diet. Will this group be followed for at least 5 years?

    Optimistically, the additional support and counseling that was provided which should improve the chances for long-term success, but a year is not enough to predict the future outcome.

    Also demonstrated through research is the hugely detrimental effect of sugar which is added to almost all processed foods. Sugar, not just because of the calories, but because of the way it is processed, leads to more fat deposition and also wreaks havoc with the body’s insulin level.

    Exercise, along with sugar avoidance, seem to be the most important components to staying healthy.

  4. Dr Sangita Bhatia

    Reduced 9 pounds weight and 3 inches in last two months by strictly leaving sugar , rice, potato and oil with one hour good workout six days in a week
    Diet taken maximum vegetables ,soup, salad and fruits
    Good luck

  5. Mark

    Over the last three months I’ve lost 22 pounds simply by upping my exercise and reducing bad calories. I’m 68 years old, always in good shape, but added sedentary pounds as I aged. (6 feet tall, 212 pounds before — 190 pounds now) I’ve generally restricted my diet to about 1200 calories a day — 200 – 300 for breakfast, 200 for lunch, and about 700 or less for the rest of the day. I try to vary the foods, do as much exercise as I can (biking, swimming, walking, weights). I drink as much non-caloric liquid as I can and I try to find food that fills me up — vegetables, fruits, mostly. I eat some cheese and a good hamburger occasionally, although I avoid most meat. I still work full time. I realize the discipline necessary, but it’s not that hard to do. I rely on a good scale and moderate my diet each day to keep a constant weight. My blood pressure has dropped from 130/80 to 117/72 and heart rate is resting 58. I’m lucky that my chronic diseases are not yet serious (osteoarthritis and borderline cholesterol, although I dont take statins because of reactions). I’m not a diet fadder, but using common sense goes a long way. Eat smart and work out. MM

  6. sharon

    A common sense approach. However, one thing missing is the AGE of the participants. This may well work for younger folks seeking to lose weight. However, not so much for those of us whose metabolisms have slowed with advancing years. Following these guidelines, which I do, does not result in weight loss.

  7. Craig Robinson

    Given that all participants in the study were overweight and “healthy”, what was not studied, and could have been very useful, was what was the impact of the two diets on participants’ blood sugars (HbA1c), insulin levels, and on some measure of inflammation. It is possible that there could have been little difference in weight loss between the two diets but big differences in the impact on risk factors related to diabetes.
    The success of the study’s two diets in sustaining weight loss is no doubt due to the excellent self-care support team. For a primary care practice the challenge is to sustain the support team to enable patients to sustain the benefits of the diet. C. Robinson at Cabin Creek Health Centers, WV.

  8. Janet Wade

    Eating is for nutrition. This study analyzes weight loss, but not nutrition. I would be interested in which diet meant people had no vitamin or mineral deficiencies. Many people who eat low carbohydrate eat few vegetables and fruit because of their carbo content. I have a difficult time believing that is healthy. The extreme, of course, is the Ketogenic diet.
    I think the best diet is SMALL amounts of everything, so we can gather different benefits from different foods.
    SMALL amounts is hard for us in the USA. WE are used to huge portions.
    I would like to know if science would back up my intuition.

    I am currently on weight watchers, because it allows small amounts of anything.

  9. Ella

    @Jack I, too, am skeptical – I don’t believe there is evidence that quick diets will do good over the long-term. Instead focusing on losing weight we need to change our mindset and aim for a healthy lifestyle. As well, I would avoid using the (buzz)word diet. It has a negative connotation and it implies restrictions.

    @Monique, I would also add the environment on that list. Make sure our physical and social environment inspire us to stay healthy. But that’s another post .

  10. Chris

    Keto diet is good for some who do moderate exercise, and I’ve used it to “jump start” some weight loss (something I didn’t have to worry about till putting on some after being injured and not exercising for 18 months).
    However, if one is going to do heavy exercise, after a week or so one “bonks,” meaning they hit the wall and have no energy, even from the fat in the Keto diet.
    Again, I have used it to jump start my diet, then a hybrid of it — still low carbs but slightly increased while at gym for a few weeks, but riding 150-200 miles a week outdoors one has to have more carbs. The good side is I am burning more. Several Saturdays ago on a 70 mile ride I burned 5000 calories. Weight is coming off.
    I did see weight loss start to happen with Keto, and it’s healthy anyone to eat less carbs, and thus low Glycemic index.
    Good luck everyone

  11. Dr Mark Rowe

    Hi Monique,
    Greetings from Ireland !
    Great article, once agin further evidence of the benefits of sustainable positive lifestyle changes
    Best wishes

    Mark Rowe

  12. Mike Flajole

    Very good article. Many of the people I work with have health issues related to type 2 diabetes so this article gives excellent direction for those struggling to manage their health condition with an appropriate diet that they can sustain. Counting calories is not necessarily the answer. Often times, people cannot understand why they just cannot lose weight or how they became diabetic or what to do about it. Thanks a lot.
    Michael Flajole Author of Diabetic and Medical Condition Life Insurance

  13. Carolyn C. Shank

    Hi Monique!
    This blog was really informative for the new-bees to start with I also want to share my experience also!
    I have been on a low crab high protein diet for last six months or so and I lost up to 12 kilos, with that diet plane I was able to lose my body fat only and as for as I think so it was really helpful for me not to lose body muscles also. I want to shair that diet plane so that other can also get there desired body shape and be happy when they look them self in mirror!

  14. Jack

    Good article Monique! While I agree with on “The best diet is the one we can maintain for life” not everyone can start eating healthy right away. In my opinion quick diets and fast weight losing methods have their own place. I studied in Harvard over ten years ago and have a plenty of love for the school and community, but you should not say no to fast diets right away. I was overweight for a long time because I just couldn’t change my habits. It was when I tried the 2 week diet plan that I started seeing results for the first time. After losing few pounds I became motivated and now I have lost a lot more weight. Even if you are skeptical I would recommend you checking it out, if you are overweight.

  15. Regiane

    have been on the low carb (Ketogenic diet) OVER A YEAR. 20-30 gr for the first 6 months, currently about 40-70 grams daily since then. maybe once a week 70-100gr; High fat (love my whole cream). moderate amount of protein. use coconut oil in decaf with the cream. Since increasing carbs the weight loss has stayed about the same +/- 5lbs but waist size increased by 1-2inches. Noticed hair loss but I don’t know if it’s stress related (husband died just before Christmas).

  16. Lorraine Marshall

    Rather than “”diet “ consider “change in eating habits “ identify vegetables that u are willing to eat as well as fruits. At meals eat a protein of choice and fill up on fruits and vegetables until u have eaten enough. You may also have one carbohydrate at each meal and drink any drink that is sugar free( seltzer, unsweetened herbal tea with lemon, coffee with cream) eat well and watch the pounds fall off! Gud luck

  17. KAT RN

    have been on the low carb (Ketogenic diet) OVER A YEAR. 20-30 gr for the first 6 months, currently about 40-70 grams daily since then. maybe once a week 70-100gr; High fat (love my whole cream). moderate amount of protein. use coconut oil in decaf with the cream. Since increasing carbs the weight loss has stayed about the same +/- 5lbs but waist size increased by 1-2inches. Noticed hair loss but I don’t know if it’s stress related (husband died just before Christmas).
    can’t do statins: recent Labs Total cholesterol elevated 300 (Yikes) but ratio is good. HDL very high (MD said he’s not seen that high in any of his pts.) and LDL very low.

    hated giving up fruit (both fresh and dried). Hate not indulging in veggies. what am I to do with the peaches and tomatoes I canned?

  18. sam

    Hi Monique, do you have any research on the Ketogenic Diet?

Commenting has been closed for this post.