Feb 22 2018

Low Fat vs Low Carb – No Difference

There is a legitimate scientific debate about the optimal proportion of macronutrients (fat, carbohydrates, protein) for weight loss and maintenance. Although I do think there is a strong consensus that the scientific evidence supports the conclusion that the proportion does not ultimately matter (within a range of healthy balance), and that all that really matters is calories in-calories out.

Since weight loss is extremely challenging, even a small edge might be worth knowing about. There are also many basic science reasons to suspect there might be a difference in hunger for different diets, and this will translate into behavior. There are further many health considerations other than just weight and it would be good to know what effect different types of diet have on cardiac and diabetic risk factors.

Unfortunately there is a great deal of confusion and misinformation out there (common for any topic of public interest). One main drivers of this, as I see it, is a self-help industry looking to make billions on the challenge of weight loss by selling one fad diet after the other. Another main driver is the media reporting basic science or preliminary studies without putting them into proper context.

That is why one of the main goals of my science blogging is to emphasize that you cannot reliably make conclusions about interventions from basic or preliminary research. Most new ideas do not work out, and extrapolating from such data is not likely to lead to conclusions which are true. We need the research to develop to the point where we have rigorous clinical trials, testing the ultimate effect in actual people.

When we consider rigorous clinical trials of the effect of different diets on weight loss, there is a fairly consistent result – proportion of macronutrients doesn’t matter. Calories in-calories out is all that matters.

Now we have one more study to add to the list. Researchers compared a healthy low fat (HLF) diet to a healthy low carbohydrate (HLC) diet in 609 participants over one year. It is a decently large trial, conducted over a sufficient time, with good design. They found:

Among 609 participants randomized (mean age, 40 [SD, 7] years; 57% women; mean body mass index, 33 [SD, 3]; 244 [40%] had a low-fat genotype; 180 [30%] had a low-carbohydrate genotype; mean baseline INS-30, 93 μIU/mL), 481 (79%) completed the trial. In the HLF vs HLC diets, respectively, the mean 12-month macronutrient distributions were 48% vs 30% for carbohydrates, 29% vs 45% for fat, and 21% vs 23% for protein. Weight change at 12 months was −5.3 kg for the HLF diet vs −6.0 kg for the HLC diet (mean between-group difference, 0.7 kg [95% CI, −0.2 to 1.6 kg]). There was no significant diet-genotype pattern interaction (P = .20) or diet-insulin secretion (INS-30) interaction (P = .47) with 12-month weight loss. There were 18 adverse events or serious adverse events that were evenly distributed across the 2 diet groups.

As with most other similar studies, one main findings was that overall weight loss was modest, although 6kg (13 lbs) is not insignificant, that is not a lot of weight loss over a year. The second main finding was that there was no difference between low carb and low fat.

This study was also looking at whether or not subgroups with certain genotypes might respond to different diets (the who, eat right for your genes, thing) and found absolutely no correlation between baseline markers of genotype and effects of different diets.

No one study is the final word, but this is consistent with the consensus of clinical trials so far. When it comes to weight loss, the only thing that really matters is how many calories you put through your mouth and how many calories you burn. For most people (unless you can maintain an athletic schedule) we can assume moderate activity level (which includes regular moderate exercise). So really if your goal is to lose weight, it comes down to math.

An average person with moderate activity burns about 2,000 calories per day. There is 3,500 calories in one pound of body fat. So, if you consume 1,500 calories per day, you will burn 500 calories of stored energy per day, or 3,500 per week, which will translate into one pound of stored body fat per week. There is no escaping this math. There is no way to hack your body so that fat melts away, or that will override your body’s basic management of energy use and storage.

All of the basic science looking at hunger, hormone levels, insulin – all of that is interesting, and may have a minor or temporary effect, but none of it trumps the basic reality of calories. They translate into insignificant effects that can be comfortably ignored. In fact, they are a distraction and focusing on things like macronutrient balance will take your eye off the real ball, the calories.

Weight loss, ultimate, is simply math. However, this does not capture the real challenge of weight management, and that is hunger. We evolved mostly in conditions of limited caloric resources. We are evolved to pack on the stored calories when we can.

In fact, a recent study confirms the finding that after weight loss our hunger increases. Our bodies respond as if we just went through a famine, and so we better pack on the fat while we can to prepare for the next one.

This is why most diets fail long term. Counting on 24/7 will power is a difficult strategy that most people cannot pull off. It is a setup for failure. What predicts long term success is making permanent changes to your lifestyle that are sustainable. Don’t count on will power, for example, have low calorie food (and not high calorie food) in the house for snacking. Change your ordering habits when you eat out. Change your perception of how large a portion is appropriate.

More importantly, find your problem areas and come up with ways to fix them. People have different behaviors, social situations, and resources, and so think about when you consume the most calories and think of ways to mitigate it that you can live with indefinitely. Weigh yourself every week, estimate your caloric intake, and keep people close to you in the loop so they can support you. All these things predict success in long term weight loss.

But don’t think that just changing the balance of macronutrients, or going on that fad diet, is the magic answer. If you do you are overwhelmingly likely to have short term success and long term failure, because you didn’t make permanent changes to your behavior.

And definitely exercise to keep up your muscle mass, metabolism, and for overall health. But don’t expect to lose weight solely by burning more calories. This strategy doesn’t work. It helps, but you need to have portion control to make the math work.

Finally, don’t plan on losing weight quickly. That is not healthy or sustainable. You are better off planning on slow but steady weight loss – 1 to 1.5 pounds per week, for example. This also predicts success.

The good news is there is a lot of research in this area and we actually have lots of helpful information that predicts success in long term weight loss. The bad news is that most of the information out there is not science-based. It is based on selling self-help books, magic diets, and wishful thinking.

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