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Does Muscle Fibre Type Determine Dietary Weight Loss?

Skeletal muscle

Skeletal muscle

Skeletal muscle, even when it is not active, is an important determinant of energy expenditure, making up 15-20% of resting metabolic rate.

But not all muscle is created equal – it is made up of varying amounts of slow Type 1 and faster Type 2 fibres, the former being more dependent on oxygen consumption and capable of endurance exercise, the latter being more capable of non-oxidative activity as in short sprints or lifting weights.

People tend to differ in the make up of their muscle fibres, which explains why some people are better at running marathons while others excel at the 100 meter dash.

But does this difference in muscle composition also affect the response to dietary weight loss?

This question was addressed by Martin Gerrits and colleagues from the University of Ottawa, in a paper just released online in the Journal of Lipid Research.

The researchers studied 26 otherwise healthy obese women who were either in the top (diet-sensitive) or bottom (diet-resistant) quintile of weight loss during the first six weeks of a medically supervised 900 kcal/day low-calorie diet program. All participants were highly compliant with the diet (meaning that they only ate 900 kcal/day) and did not differ in levels of physical activity. Subjects were matched for both age and initial BMI.

While the diet-sensitive group lost 11.4 kg, the diet-resistant group lost only 7.5 kg during the first 6 weeks. This translates into an almost 25% or 350 kcal/day lower caloric deficit in the diet-resistant group.

Following program completion and weight stabilization, skeletal muscle biopsies showed a higher proportion of oxidative Type 1 fibres in the diet-sensitive compared to the diet-resistant women.

Gene expression analysis also showed upregulation of genes involved in oxidative phosphorylation, glucose and fatty acid metabolism in the diet-sensitive group.

Thus, these data support the notion that the rate of weight loss in response to dietary caloric restriction may very much depend on your muscle composition.

Clinically, this would mean that people who are better at aerobic (endurance) exercise may find it easier to lose weight than people who are better at anaerobic exercise (sprints or lifting weights).

Perhaps the reason that people who combine diet with endurance exercise tend to lose more weight than people who prefer resistance training has more to do with their muscle composition than with their choice of exercise (or the calories burnt doing it).

Edmonton, Alberta


  1. I think it is important to note here that fiber type of the vastus lateralis and rectus femoris aren’t necessarily an indication of overall fiber type for an individual.

    However, if fiber type does influence weight loss, this could be good news since it is well known that fiber type shifts are possible with exercise. Conversion from less oxidative types of type 2 fibers to more oxidative types of type 2 fibers is possible with endurance training suggesting that we may be able to influence this process.

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  2. “Perhaps the reason that people who combine diet with endurance exercise tend to lose more weight than people who prefer resistance training has more to do with their muscle composition than with their choice of exercise.”

    I enjoy both endurance exercise and resistance training — but find that it takes me a long warm-up to be able to get to the point where interval training is enjoyable. I usually can only do “bursts” after at least 30-45 of relatively low-intensity but consistant exercise. I probably function best on about 2 hours of moderate, intense and/or resistance training a day, but as a working mom of a young child, I rarely have that kind of time. I could use an exercise physiologist — and an extra hour a day to be training — why isn’t that covered by my job/health insurance, but bariatric surgery is? Also, when I’ve engaged in what feels like my ideal amount of activity, 1.5-2.5 hours a day which includes moderate and bursts of high intensity as well as strength, I do tend to feel rather hungry the next day. I don’t mind eating — it’s just not proven possible for me to simultanously increase my activity to that level and decrease the amount of calories I take in. Weight loss isn’t my main concern, managing diabetes is.

    I recall an interview with a ballerina who found the shape of her strong legs and glutes could be altered by shifting the hours she spent dancing to include time spent doing pilates. What has been studied as a way of shifting fiber types? I don’t care for pilates but maybe there are other modalities that I would be interested in.

    Hey, does anyone want to study me? I am a willing guinea pig with lots of type 2 fibers! I don’t care so much about changes in weight as changes in metabolic function (with weight loss as a potential side effect).

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  3. Ancel Keys study in the 40s on conscientous objectors of war who volunteered to severely restrict their calories described just such variety in the rate of weight loss. Yet health professionals continue to tell people that 3500 calories is equal to one pound of fat and that we should all be eating a low fat, high carb diet. Nutrigenomics research has confirmed that we are not all equal and that a one size fits all approach is bound to fail many people. For many years I at according to Canada’s food guide and only became fatter from the grains. It wasn’t until I switched to a high fat, high protein diet that I was able to lose body fat. My activity pretty much stayed the same, very high – 1-3 hours per day, with both aerobic and anaerobic exercise using both type 1 and type 2 fibres so I can only assume that it was the change in diet that affected my changes in body composition.

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  4. What diet did they follow? I believe the diet can be tailored to the individual helping the type 2 individual to lose more and maybe helping the type 1 individuals to lose even more.

    The individuals with more type 1 fibres have a higher capacity to burn fat for energy but a lower capacity to burn carbs so would benefit more from a lower carb intake and higher fat in take. The opposite would be true for the type 2 individuals.

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  5. I must have a high proportion of type 2 muscle fibers: I’ve benefited more from vigorous intensity workouts – like circuit training and high intensity interval training – than from moderate intensity workouts like brisk walking. I’ve attempted to jog in the past, but I’ve never had the endurance to persevere. This might explain why I’m more prone to gain weight.

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