The DIETFITS study that came out recently was excellent. Like really excellent. It's been shared around by others like Alan Aragon but I wanted to review it in depth because I loved it.
Some studies have been coming out showing what diet is best for someone might be based on genetics or how they respond to insulin, and this study looked at that. It also looked at whether low carbs or low fat did better in general for weight loss and some other markers of health. In the past we've seen no difference in weight loss between the two in well controlled trials, but we have seen small differences in some other metrics. There has also been huge variance in between subjects in some studies and how much they lost using the same methods. We've seen instances where those with insulin resistance do better on low carb diets in past research, and anyone with experience helping people lose weight has probably noticed the same trend. Someone correct me if I'm wrong, but anecdotally I think my peers will mostly agree that those on the sedentary obese side of the spectrum tend to do better on lower carbs, while those who are leaner and more active usually do better on higher carbs. We also all know some people who are the opposite.
Usually finding what diet works best for someone when working with them takes trial and error, and that can be very bad for motivation. For those who are trying to lose weight on their own it can be disastrous. One of the biggest problems with the popularity of fad diets is they're usually unsustainable so they set people up for failure. Then when the people fail they think they didn't have the mental fortitude, or dieting is just too hard for them so they give up. Obviously this isn’t everyone, but most of us probably know someone this has happened to.
That issue isn't just with fad diets though, it also extends to any diet that isn't right for the individual. If trying to adhere to a low fat diet makes you miserable you're being set up for failure by trying it just like a fad diet would do. If you feel tired all the time and can't sustain energy for daily activities and working out on low carbs you aren't likely going to succeed on that either.
Losing weight isn't easy for most people, even with the right plan. Without the right plan it can be nearly impossible. All of the more recent research coming out on dietary methods is advising an individualized approach instead of a single ideal dietary method for everyone. In practice this is what good coaches have been doing for a very long time. Finding a way to determine what diet someone would do best on before even starting a diet would be enormous, it would remove the trial and error portion that can be demotivating and even lead to a way people not working with a professional could properly individualize their diet to themselves without needing much background knowledge at all.
However things aren't usually that simple.
This study tested whether genetics dealing with how people metabolize fat and carbs affect what diet they do better with. They grouped people by 3 genotypes, low fat, low carb, and neither. They also looked at level of insulin sensitivity and interaction with success on either diet. Insulin sensitivity refers to how well your body handles insulin, and insulin resistance is when your body doesn't handle it properly. Weight gain is a large driver of insulin resistance so the overweight and obese often end up with it, and insulin resistance can lead to metabolic syndrome which comes with more complications.
They ended up looking at data from 609 people after exclusions applied. They were all between 18 and 50 with a body mass index between 28 and 40, so mostly in the obese category. They excluded anyone with serious health issues or on medication that would affect results.
They were put into either the low fat or low carb group randomly. The subjects attended classes in groups on how to eat a healthy diet that fit their group, starting with weekly and getting less frequent as the study went on. They attended 22 classes total, and each class was comprised of the same people each time. They wanted the subjects to benefit from the social component of the groups and feel comfortable in the classes without being intimidated by new people they hadn't seen before.
The fact they stressed a healthy diet is awesome, because minimizing a difference in diet quality between the groups make comparisons much more accurate. Low carb diets can be great at reducing calories even when eating ad libitum, but they also cut out a lot of the hyperpalatable foods that people tend to overeat. Overeating on a low fat diet based mostly on healthy sources is how people should be doing low fat diets, so it's nice to see that stressed. Low quality low carb diets can also lead to issues with ldl and other things, so keeping it healthy should show any advantages low carbs diets might have well.
The trial lasted a year. They wanted the diets to be as different as possible in regards to carbs vs fat. They expected the subjects to go off track to a degree so they thought if they started with as large a difference as they could the difference would still be significant after a year. They attempted to match difficulty of the diets as well, which surprisingly a lot of other studies haven't even considered. And like I already pointed out, they stressed the overall healthiness of the diets, focusing on nutrient density.
The dietary instructions the people were given allowed a high level of individualization for the subjects and were designed so each subject could find what works for them. It was very similar to methods many good coaches use, which isn't real common in largish studies like this.
They focused on three things in the classes. The first I've already mentioned a couple times, being dietary quality. The whole length of the study they stressed making healthy food choices for both groups. Both groups were instructed to eat mostly whole foods and prepare them at home as much as possible. They were told to avoid processed foods and foods with refined sugars, white flours and trans fats. They were both told to eat as many veggies as possible with flexibility in how they prepared them due to their own preferences. They were even given instructions on how to order healthier food when eating out, like ordering salad dressing on the side for the low fat group or greens instead of mashed potatoes for the low carb group. The low fat group was instructed to choose whole grains, beans and legumes, fresh fruit, low fat dairy products, and lean meats. The low carb group was instructed to choose healthy oils and fats, avocados, hard cheeses, seeds, nuts, and nut butters. They even provided instructions on how to eat healthy within their budget, since some of the foods they recommended were expensive. They weren't given any calorie limits or macro percentages to stick to, they were only given instructions on how to manipulate either fat or carbs depending on their group.
The second and third things they focused on were consecutive rather than consistent from the beginning to the end. The first 8 week phase they called "limbo," in reference to seeing how low they could go on carbs or fat, and instructed the subjects to lower their carbs or fat to 20g over time if they could. They weren't given a specific goal on how long it should take outside of the 8 week end of the phase. So lowering to 20g over the course of one week wasn't considered better than taking 8wks to do it. They were also told it wasn't real important whether they got to 20g or not, they just wanted them to get as low as they could. Once they got to that point they were instructed to maintain it for at least a few weeks to see if they could consistently adhere.
The third aspect, and second phase of the study, was the "titrate" phase. In this phase they were instructed to slowly add fat or carbs back into their diets 5-15g at a time and monitor their satisfaction and weight loss progress with each level for a week or longer. Then they could decide to either stick with that level another week or add in more. They were told the goal is to find the lowest level that they could adhere to long term, even beyond the end of the study, so they weren't to add more when they think they have enough to keep progressing. They were also able to lower them back down if they thought they could go back to a lower intake.
Another amazing thing about this study is that the subjects were told that the study was looking at differences between how the right diet varies in between individuals, so they expected wide variance in how well people succeeded in each group. This is a big deal because of what I talked about earlier. When people fail on diets they commonly think they’re failing because they aren’t strong enough, or committed enough, and end up feeling like they’re a failure for failing. Letting the subjects know they expect some to not do so well and that it’s due to differences in what diet works for what person and not because they’re just a failure is a great thing for the subject’s mindsets.
They didn’t only discuss the actual diets with the subjects in the classes either, they also discussed other factors important to weight loss including behavior, emotions, and physical activity. The classes were usually primarily nutrition with focus on one of the other aspects each session, although most sessions touched on all 4. The beginning was the most nutrition focused and more focus was put on the other aspects over time.
The overall goal was to help the subjects overhaul their diet to something that would be sustainable long term. This is a huge thing as well, a lot of people see dieting as a temporary thing to reach a goal and don’t have a plan for when they reach that goal. It’s also important to learn healthy habits while dieting. A lot of the things that allow people to maintain results are related to changing behaviors and habits, and that takes time. Learning the habits you need to maintain results while losing weight sets you up for success when it comes time to maintain.
The specific topics they covered were excellent as well. They actually touched on a lot of the things I write about and things Spencer Nadolsky wrote about in “The Fat Loss Prescription,” which is my favorite book to recommend to help the general population lose weight. They had classes about mindful eating, food and mood, sleep and weight, food addiction, exercise, and tips for shopping and cooking.
They were given a lot of attention and help beyond what I’ve already mentioned too. They were given recipes in a newsletter, emails reminding them of classes before classes and summaries of the classes afterwards, and the instructors even reached out to individual subjects as needed. They were also able to post questions or comments to the group or to an instructor personally. As I said earlier, this study utilized a lot of the same strategies good coaches utilize with clients.
As far as exercise they were instructed to aim for quite a bit of moderate to intense physical activity, 60-90 minutes a day. They were told to work up to this during the first 3 months if they weren’t already at that level, starting by adding 10 minutes or so to their current amount, and use a combination of cardio and strength training. Going along with the sustainability theme they were told to find practical ways to be active that they actually enjoyed so that they would be able to continue it long term.
The psychological portion was excellent as well, utilizing methods shown to be effective in helping people make sustainable behavior modifications. They highly stressed the idea that the best diet varies between people, and also addressed things like goal setting, relapse prevention, supportive environments, and healthy self reinforcement and rewards.
The subjects rated the enthusiasm and knowledge of the educators highly, 4.6 on a scale of 1-5. Both groups ended up decreasing calories about the same amount even without any calorie goals. They were 500-600 calories below baseline, which is a common calorie deficit to diet on. The low carb group averaged 96g carbs after 3 months, 113g at 6 months, and 132g at 12 months. This range falls in the range some studies have been recommending as a good balance of low enough but not too low, and since this study was designed to find that balance for individuals it backs those up. The low fat group averaged 47g at 3 months, 50g at 6 months, and 57g at 12 months. The fat intake in the low carb group and carb intake in the low fat group stayed pretty stable at all points.
The average weight change wasn’t significantly different, -11.6lbs in the low fat group and -13.2lbs in the low carb group. As expected, the variance between individual weight loss in both groups was large, with some losing up to 66lbs and some gaining up to 22lbs. This isn’t real surprising. It’s notable that the losses were more than 5% of baseline bodyweight, which is regarded as a threshold for significant positive effects.
A bit more surprising is that neither genotype nor insulin status was significantly associated with success on either diet when people were matched or mismatched to the one prior studies have shown could work better. There were also no differences between groups for body fat percentage, waist circumference, or body mass index. Both diets improved lipids, blood pressure, insulin and glucose levels. LDL did increase on the low carb diet tho, which isn’t real surprising with the increase in fat without any decrease in saturated fat. HDL and triglycerides improved more on the low carb diet. Both groups showed a similar decrease in metabolic syndrome. Resting energy expenditure decreased more in the low carb than low fat group, but it wasn’t statistically significant. Interestingly total daily energy expenditure actually went up a bit in both groups with no difference between groups. That shows even after 12 months and the lower resting energy expenditure the higher level of activity kept total calorie burn up compared to baseline. This is important for sustainable results, as studies have shown continuing exercise after losing weight is a big predictor for successful weight maintenance.
The authors speculate their finding differed with prior studies looking at insulin response and genotypes because the prior studies were small and short term. Not all other studies have found the same either. They also speculate that the focus on healthy diets in both groups minimized differences, which is something nutrition professionals have been speculating quite awhile.
This study is just more evidence that the proper diet for someone is very individual, and we really don’t have a good way to guess what will work for who until trying. It also utilized many of the successful methods coaches have been using for quite awhile, and a lot of people were successful. It’s very important to let people know there isn’t a one size fits all diet, and it can take some trial and error. When people realize this they’re less likely to give up or feel like a failure due to trying one that’s bad for them. Hopefully more future studies take note of these methods and apply a lot of them, as far too many studies have a significant disconnect between study design and what is successfully applied in practice.
If anyone wants a link to any of the studies I alluded to but didn’t cite let me know.