1. Certain Foods Increase Metabolism and Help You Lose Weight
While a range of foods or their derivatives may affect metabolism to some extent, this needs to be placed in perspective. Food products proposed as weight loss aids include green tea, black tea, chili (capsaicin), ginger, coffee, caffeine, calcium, conjugated linoleic acid, medium chain triglycerides, fish oil, flax oil, extra protein, various herbs and spices and no doubt many others.
Although consuming these foods is almost certainly not harmful, and may even help with a small amount of weight loss, my main objection to this approach is that it tends to detract from the central theme of weight loss, which is to eat less and exercise more. Using manufactured supplements based on these products is not the way to approach functional weight loss foods either. Guaranteeing supplement product quality and efficacy is a perennial problem even when there is a proven effect of the whole product.
It’s not that these products are completely useless, it’s just that claims for fat loss are usually highly overstated and you will be better off concentrating on the larger picture of calorie restriction and exercise.
2. People who Eat Breakfast are Slimmer
This appears to be true. The US National Weight Control Registry reported that successful long-term weight losers and maintainers shared a number of characteristics including a low-fat diet, regular cereal breakfast consumption and regular exercise. This has been supported by other studies in which eating breakfast, especially a cereal breakfast, is associated with a lower body mass index.
The reasons for this are probably to do with how a breakfast meal establishes patterns of eating or overeating for the following meals.
3. Carbohydrates are Fattening
This is one of those infuriating qualified truths that has become an absolute truth for some weight loss and exercise pundits. The answer is that if you eat in excess of your energy requirements, including physical activity, the excess will get stored as fat. This applies to carbohydrates as much as fat and protein, although protein has a slightly higher metabolic cost than carbohydrate which in turn has a higher metabolic cost than fat. A ‘metabolic cost’ is the amount of energy that a particular food requires for the body to unlock and use the energy contained in it.
Excess protein can be broken down to carbohydrate which in turn can get converted to fat. That’s essentially how the excess end up stored as fat. If you are in energy balance – when you consume as much as you expend – you won’t put on weight. It can be somewhat more complicated than that, but that’s the elementary physical law, and you can’t get around it. Carbohydrates only make a contribution to fat storage if you consume an excess of calories over requirements. Even if some carbohydrate is stored as fat intermittently, which can occur depending on the dynamics of your diet, that fat is still available for burning as fat fuel and will not contribute to weight gain if your energy intake and expenditure is balanced. Get the picture?
4. Extra Muscle Can Help You Lose Weight
This is another qualified truth masquerading as an absolute truth. Let’s take a look at this.
Muscle uses more resting and exercising energy than fat, so replacing fat with muscle should help you lose weight, right? Not necessarily. Firstly, the difference is not that great because fat also has an energy cost. Reliable estimates are that one extra pound of muscle, about 500 grams, uses less than 10 extra calories per day when it replaces fat. That’s a jellybean or two. Sure, muscle protein turnover and extra oxygen consumption during and after muscle building exercise will add to this energy expenditure.
However, if you are trying to lose fat weight, the best you can probably hope for is to maintain muscle with weight training. Increasing muscle while losing fat is very difficult to do. And resting metabolic rate -- the amount of energy you use when sitting on the couch -- drops when you lose weight and rises when you put on weight even if it is fat.
Christian Finn has a good article on the subject of muscle, fat and metabolism.
To sum up, weight training is excellent for maintaining muscle in a fat loss phase. Aerobic exercise tends to consume more calories so you should include that as well. My circuit training program is a good example of how they can be combined in a circuit.
5. Some Diets have a Metabolic Advantage for Weight Loss
Do low-carb, low-GI, or low-fat diets have some inherent advantage other than just calorie reduction that help us lose weight? To make this proposition clearer : do some dietary patterns help you lose weight beyond what you would expect from reducing food intake?
The general answer is: 'not much' -- total food calories are still the main determinant over the longer term, even accounting for some small metabolic advantage for higher protein consumption. For example, the Atkins low-carb diet tends to provide more rapid weight loss in the short term, yet at 12 months weight loss is about the same as with more conventional diets.
The qualified answer is that some dietary patterns may make you feel less hungry after a meal and result in lower consumption over a 24-hour period. Diets high in fiber and perhaps low in glycemic index, and diets somewhat higher in protein may provide this advantage. Combining low fat with higher protein and fiber rich fruit, vegetable and whole grains may be the best combination of all for weight loss.
Pirozzo S, Summerbell C, Cameron C, Glasziou P. Advice on low-fat diets for obesity. Cochrane Database Syst Rev. 2002;(2):CD003640. Review.
Foster GD, Wyatt HR, Hill JO, McGuckin BG, Brill C, Mohammed BS, Szapary PO, Rader DJ, Edman JS, Klein S. A randomized trial of a low-carbohydrate diet for obesity. N Engl J Med. 2003 May 22;348(21):2082-90.
Geliebter, A., M.M. Maher, L. Gerace, et al. Effects of strength or aerobic training on body composition, resting metabolic rate, and peak oxygen consumption in obese dieting subjects. Am J Clin Nut 66: 557-563, 1997.