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Why Quality Trumps Quantity When It Comes to Diet


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For years, researchers have debated which diet is best for weight loss: low-fat or low-carb. Now, a robust long-term study has settled the question once and for all. The answer? There’s no one-size-fits-all, but any weight loss diet should emphasize real food. Read on to learn more.

Quality over quantity in diets
The quality of the food in your diet is often way more important than the quantity of the food you eat. istockphoto.com/mapodile

Obesity is a major public health epidemic. Forty percent of adults are already obese, and if current trends continue, more than half of adults will be obese by 2030. (1) Obesity is associated with an increased risk of heart disease, diabetes, and cancer and presents a massive $147 billion burden on the healthcare system each year. (2)

Researchers have long debated whether low-fat or low-carbohydrate diets are best for weight loss. Regardless of the macronutrient content, however, most long-term studies have reported little success in achieving and maintaining significant weight loss.

In 2016, I wrote an article called “Carbohydrates: Why Quality Trumps Quantity,” in which I argued that the answer to obesity and metabolic disease lies not in how much carbohydrate we eat, but rather what types of carbohydrate we eat.

A new study found that people who cut back on added sugar, refined grains, and processed food lost weight over 12 months—regardless of whether they were low-carb or low-fat. #paleo #optimalhealth #chriskresser

A landmark study recently published in the Journal of the American Medical Association supports this argument and suggests that the same principles apply to fats. The researchers found that on average, people who cut back on added sugar, refined grains, and processed food lost weight over 12 months—regardless of whether the diet was low-carb or low-fat. (3) In this article, I’ll break down the methods and findings of the study.

Treading Where Few Researchers Have Gone Before

Nutrition science research is already fraught with problems, and weight loss studies bring their own unique difficulties. In order to produce a robust weight loss trial, an aspiring research group must:

  • Have enough funding to support a large scale randomized trial
  • Recruit and retain a very large group of subjects
  • Collect data over a long-term period
  • Ensure subjects are complying with the dietary intervention

Ideally, they would also use weight loss strategies that can be applied and sustained by free-living people. Unfortunately, few, if any, studies published in the literature have succeeded in meeting all four of these criteria—until now, that is. In February, the results of a long-term, large-scale, randomized clinical trial led by Dr. Christopher Gardner, Director of Nutrition Studies at the Stanford Prevention Research Center, were published in JAMA.

The Study Design: Whole Foods Low-Fat vs. Low-Carb

The scientists recruited 609 adults to participate in the 12-month study. The subjects were both male and female, were between 18 and 50 years old, and had an average body mass index of 33 (class I obesity). Those with uncontrolled metabolic disease were excluded from the study. The researchers randomly split them into two diet groups: “healthy low-carb” and “healthy low-fat.”

During the first eight weeks, participants in the low-fat and low-carb groups were instructed to reduce intake of total fat or digestible carbohydrates, respectively, to 20 grams per day. They then slowly added fats or carbohydrates back into their diets until they reached the lowest level of intake that they believed they could sustain indefinitely. Additionally, both diet groups “were instructed to 1) maximize vegetable intake; 2) minimize intake of added sugars, refined flours, and trans fats; and 3) focus on whole foods that were minimally processed, nutrient dense, and prepared at home whenever possible.” (4)

For example, foods like fruit juice, pastries, white rice, white bread, and soft drinks are low in fat, but were not recommended to the low-fat group. Instead, the dietitians encouraged participants to eat whole foods like lean meat, brown rice, lentils, low-fat dairy products, legumes, and fruit. Meanwhile, the low-carb group was instructed to focus on foods rich in healthy fats, like olive oil, avocados, salmon, cheese, nut butters, and pasture-raised animal products.

The best part? The participants were told not to worry about counting calories or limiting portion sizes, but to simply eat enough to avoid feeling hungry.

Both groups attended 22 instructional classes led by registered dietitians over the course of the 12 months to help support them in these changes. Overall, 79 percent of the participants completed the trial. At the end of the year, average macronutrient breakdown by energy was as follows:

Low-fat group: 48% carbohydrate, 29% fat, 21% protein
Low-carb group: 30% carbohydrate, 45% fat, 23% protein

This was determined by random 24-hour dietary recalls, but was also confirmed with more objective measures of compliance to the diet, like respiratory exchange ratio.

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Weight Loss without Calorie Counting or Restriction

The results? Both diet groups eating a whole-foods, nutrient-dense diet spontaneously reduced caloric intake and lost significant weight in the year-long study. However, there were no significant differences between the low-carb and low-fat groups in regard to weight loss, body fat, or waist circumference. On average, the low-carb group lost 13.2 pounds (6 kg), while the low-fat group lost 11.7 pounds (5.3 kg).

This might not seem like a dramatic amount of weight loss, but according to the National Heart Forum, even a modest (5 percent) reduction in body mass index could spare the lives of millions of Americans and save billions of dollars in healthcare costs. (5)

Indeed, both groups also experienced improvements in other health markers. After 12 months, participants had reduced fasting glucose, insulin, and triglycerides and improved systolic and diastolic blood pressure. In fact, 36 participants in each group that had metabolic syndrome at baseline had improved their health so much that they no longer fit the diagnostic criteria for metabolic syndrome.

Just to reiterate, there were no differences between low-carb and low-fat. When the subjects focused on real, whole foods and cut refined grains, sugars, and processed foods out of their diet, they lost significant weight, without having to count calories or restrict energy intake. However, this was based on averages, and does not mean that an individual might not respond better to a low-carb or low-fat diet.

Open Questions and Future Directions

This study represents an incredible effort by the researchers and fills an important gap in the scientific literature. Still, any study worth its marbles will inevitably create some open questions:

Why did some people lose weight and others didn’t? While participants on average lost weight in both groups, there was a huge variability in individual responses: some lost up to 50 pounds, while a few gained weight. The researchers hypothesized that individual responses would depend on genetics or insulin response to carbohydrates, but the data didn’t support this idea. Thus, the elusive factor that determines success in weight loss is still unknown. (I heard through the grapevine that they also collected fecal samples in this study, so analysis of the gut microbiome may offer some clues.)

Was the low-carb group truly low-carb? Despite starting off at a carbohydrate intake of about 20 grams per day in the first two months, the low-carb group was already consuming 97 grams per day by three months, 113 grams per day by six months, and 132 grams per day by 12 months (including 22 grams of added sugar). In other words, while they started the trial on a very-low-carb diet, by month 12, they were consuming more of a moderate-carb diet. It’s conceivable that sustained ketosis could have sparked greater weight loss in the low-carb group. However, the subjects were instructed to eat the lowest amount of carbs they could sustain over time, and most found that ketosis was simply unsustainable.

Will both groups keep it off? It will be interesting to see the five-, 10-, and 15-year follow-ups of this study, to see how many people in each group were able to successfully keep off the weight they lost. If they stick to a whole-foods way of eating, my guess is that they might!

“Western” Diets vs. Ancestral Diets

Not too surprisingly, the findings from this study align with what we see in populations eating a more ancestral diet. Among traditional cultures, fat and carbohydrate consumption vary widely, yet obesity is essentially nonexistent. The Inuit, Masai, Turkhana, and Kavirondo consume up to 58 percent of their daily energy from animal fat, yet are lean and have excellent metabolic health. (6) Likewise, the Kitavan Islanders of Melanesia consume 60 to 70 percent of their daily energy as carbohydrates from fruit and tubers (7), yet boast healthy levels of insulin and blood glucose (8, 9) and have a virtual absence of obesity. (10)

These people don’t just have superior genetics. Inuit that have left their traditional lifestyle for a Western diet and lifestyle also left their protection against cardiovascular disease behind. (11) Similarly, Kitavan Islanders who leave for the mainland and begin to eat a Western diet quickly become overweight. (12)

What We Can Learn from This Study

Altogether, this new research adds to anthropological data to clearly show that the quality of food is far more important than the macronutrient composition. Here are the overall takeaways from this article:

  1. Eat real food for weight loss. Focus on fresh, whole foods that are minimally processed, and eat mindfully, stopping when you’re full.
  2. Self-experiment. The study described here found that on average, there were no differences in weight loss between the low-fat and low-carb groups. However, it doesn’t mean that a single individual won’t fare better on one diet versus another.
  3. Consider life stage and underlying conditions. This study was performed on obese adults without major underlying conditions. If you are pregnant, lactating, or have poor thyroid function, you probably still need a moderate to high carb intake. If you have diabetes, a lower-carb diet may help manage the condition.
  4. Get support. This study also provides evidence that access to regular support from dietitians or health coaches can help people make lasting behavior change and improvements in their health.
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Join the conversation

  1. I wholly agree that any diet should consist of healthy whole foods, but the “landmark” study cited here is not very helpful.
    This study seems designed to reach the desired conclusion. Neither the “low fat” diet nor the “low carb diet” they used would be recognized as such by proponents of those diets.

    For the low fat diet, 29% of calories are coming from fat (Dean Ornish defines a low fat as less than 10% of calories coming from fat diet); and for the low carb diet, 30% of calories are coming from carbs (low carb proponents usually call for well under 10% coming from carbs, and zero from starches). Really these are just bookends of the standard American diet.

    If the researchers really wanted to answer the question they would use diets designed by the proponents of those diets that are clearly distinct.

  2. Chris, to expand your point, I take this even further; it’s been my mantra for a number of years now.

    It’s not so much what you’re eating and doing to eat/live a healthy lifestyle, it’s just as important to know and understand what you’re NOT EATING and NOT doing. A couple quick examples:

    Does it really matter if you exercise on a treadmill, do Pilates, walk your do or kick-boxing – OR does matter that your moving and exercising and NOT sitting on the couch eating cheetos and binge-watching episodes of the Walking Dead?

    Should I freak out because I ate a whole banana with 11g of sugar? Or get frustrated whether or not to have that wild caught salmon rather than going with home made chicken soup tonight? Does it really matter if you have quinoa, or wild black rice as your carb for dinner?

    Think about this. Or is it just common sense that it’s 100% better to NOT be eating Kraft Man-n-cheese with a double dose of canned cheese sauce, deep fried manufactured chicken fingers and a 32 oz coke?

    It’s what you’re NOT eating and NO LONGER doing that matters. Choose whole and natural foods and worry less about counting calories, carbs and fats, and worry more about just living healthy.

  3. I would like to see a carnivore diet! No, I’m not kidding. This is one of those studies where anything could be happening. Having not read it I hope they were doing weight and blood sample at ramdon times otherwise you know what happens, people say oh crap, I uave a weigh in coming so I had better get to the gym and starve myself. Essentially little to no control and no discipline by the folks eating the diet really tells us nothing.

  4. I find this a very interesting contribution to the complexities of elements of dietary intake for an individual person. It is good to hear that one rule does not always fit all.
    I would very much like to hear your comments on the work of Dr Eran Elinav and Dr Eran Segal of the Weizmann Institute of Science if you have come across it and if you would like to comment.
    Thank you for your columns,
    Best wishes, Janet Pollak

  5. What role could/does Mastocytosis play a role in GI symptoms and what to do about it?

  6. I agree with the bottom line conclusion that eating real food of one sort or another will be most effective for a wide group of people. However, low fat dairy is generally a pretty refined food, and high fat oils may also fall outside a real food category. The latter examples may explain why there was no weight loss for some. And many people are never going to thrive or improve on low fat, particularly if already overweight . . . I found myself in this latter camp. In sum, I think the real food message is important and should emphasize a wide spectrum of approaches may work based on the individual.

  7. My tribe (my family) and I follow seasonal eating patterns that allow us to slip in and out of ketosis. If we’re feeling really good, we may stay in it a little longer. It helps us to think, to perform, and to produce. We also go through periods of feast and famine with 24 to 120 hour fasts, and huge refeeds, where almost nothing that resembles primal food is off limits.

    I believe water fasting (only consuming water and minerals) is likely the single, most powerful metabolic intervention in existence… it’s accessible to everyone… it’s time and money saving… it’s the default way of life in the animal kingdom… Only recently have certain animals (Sapiens included) had such easy, unlimited, no effort required, access to food. Can’t figure out how to heal and be healthy… consider a 5-day water fast to address root cause issues. Do it as needed… sometimes wife and I do it once a month because it’s awesome! No, this is not medical advice but it is the way animals, including humans, have healed for millennia upon millennia… it still works in the modern world too. No instructions required… all you have to do is not eat but if you’d like some hand holding, read or Audible “The Complete Guide to Fasting” by Jason Fung and Jimmy Moore.

    • “…but it is the way animals, including humans, have healed for millennia upon millennia… it still works in the modern world too. No instructions required… all you have to do is not eat but if you’d like some hand holding, read or Audible “The Complete Guide to Fasting” by Jason Fung and Jimmy Moore.”

      HAVE YOU SEEN JIMMY MOORE? He does not look healthy.

      • Jimmy Moore may very well be metabolically healthy. Subcutaneous fat in and of itself is not a significant risk factor.

  8. Chris – Great synthesis of the current study. I’ve been involved with LC, HC, LF, Paleo, etc… dieters for nearly 10 years now, it truly does seem to boil down to what the researchers instructed the participants to do:

    “1) maximize vegetable intake; 2) minimize intake of added sugars, refined flours, and trans fats; and 3) focus on whole foods that were minimally processed, nutrient dense, and prepared at home whenever possible””

    This eating style has been my mantra for the past 7 years, and I truly feel I have found freedom from perpetual dieting and weight struggle. While the occasional Cadbury’s Easter egg finds its way into my mouth, it is very easy to make wise food choices most of the time. I think that focusing on macronutrients leads to overthinking and failure of diets that restrict carbs or fat.

    Thanks for your continued writing on these topics.