Do low-fat diets really make us fat?

Proponents of high fat diets often support their claims with data which shows that the percentage of energy consumed from fat has decreased over the years, while at the same obesity has increased. They extrapolate this to mean that low-fat diets are promoting obesity.

A recent study in the Journal of the American Dietetic Association sheds more light on this matter. It investigates the difference in fat intake in the United States between 1989/1991 and 1994/1996 using data from their national nutrition surveys. It also looks at the difference between looking at fat intake in actual gram amounts versus percentage of total energy intake from fat.

Over the seven-year period investigated, it found that percent of energy consumed from fat did indeed decline, however the actual grams of fat consumed increased (by a mean of 3g per day per person). How could this be? Well, because total energy intake increased a lot more than fat intake increased, this caused the percentage of energy from fat to decrease proportionally.

What this study tells us is that in the United States total energy intake is increasing, with the majority of this increase being from beverages (mostly soft drinks), food mixtures (grains mixtures or meat mixtures), grain snacks (crackers, salty snacks), and pastries (cakes, cookies, pies, quick breads). Total energy intake increased from a mean of 1,878 to 2,056 calories, with soft drinks increasing the most, from a mean of 76 to 107 calories per day. So not only is energy intake increasing, but much of it is coming from foods with low nutritional value.

At the same, other studies show us that energy expenditure and exercise has decreased – leading to an energy surplus which the body stores as fat. The moral of the story is that low-fat diets do not make us fat - eating too many calories for the amount of energy that we expend does.

Chanmugam P, Guthrie JF, Cecilio S et al. Did fat intake in the United States really decline between 1989-1991 and 1994-1996? J Am Diet Assoc 2003; 103: 867-872.

What does technology have to do with obesity?

A paper published by the American National Bureau of Economic Research took a look at the link between obesity and technological change. They used mathematical equations to prove that as society has developed, exercise has become less available and also more expensive. Instead of being paid to do physical labour, such as in an agricultural or industrial society, we are now having to pay in order to exercise. They state that "in many ways, obesity is a side effect of prosperity". We are able to buy machines or pay others to do our manual work making us more sedentary. At the same time more food is available and we are eating more energy dense food.

In the study, they also calculated that over a lifetime a person who works in a sedentary job will end up with a body mass index 3.3 units higher than someone in a highly active job.

Humans were designed to be moving all day, not sitting at a desk for hours on end, moving out of the chair for an occasional drink or call of nature. It is now up to us to make the effort to increase our activity levels, start moving more, and burn up some of those calories we are saving for a rainy day.

Lakdawalla D, Philipson T. The Growth of Obesity and Technological Change: A Theoretical and Empirical Examination. National Bureau of Economic Research. http://www.nber.org/papers/w8946.

How NEAT are you?

Non-exercise activity thermogenesis (NEAT) is the energy our bodies use up for everything we do except eating, sleeping and exercise. Increasing our amount of NEAT increases energy expenditure, which means more calories burned. The body also has the ability to burn up short term excess calories by increasing NEAT (long term excess leads to weight gain). However, there is a lot of variation between individuals in how much their bodies actually do this. It is thought that in people who gain weight easily, NEAT is not increased as much when they overeat, which leads to quicker weight gain.

In days gone by, when manual work was more common, levels of NEAT were high. These days, where sitting at a desk is more common, levels of NEAT in daily life have become much lower. For example, standing uses up more NEAT than sitting. Another study which investigated NEAT and fidgeting found that people who fidget have increased NEAT and therefore burn up more calories. Which leads to the question of how long it will be before someone develops The Fidget Diet!

Levine JA, Eberhardt NL, Jensen MD. Role of nonexercise activity in resistance to fat gain in humans. Science 1999; 283: 212-4.

Levine JA, Schleusner SJ, Jensen MD. Energy expenditure of nonexercise activity. Am J Clin Nutr 2000; 2: 1451-4.

Breakfast - is it the most important meal of the day?

Breakfast is an often overlooked meal - lack of time or lack of hunger are two common reasons. In some cases, people skip breakfast in order to try and lose weight. Unfortunately, this can have the opposite effect. Studies often show that those who skip breakfast weigh more, with recent research adding further weight to this argument (no pun intended). In this study, 500 people had their diet assessed by dietary recall five times over a one-year period. Those people who regularly skipped breakfast were a whopping 450% more likely to be obese (adjusted for total energy intake and exercise levels). They also found that eating four or more times per day was associated with a lower risk of obesity than eating three or fewer times per day.

This may not seem entirely logical to people who are trying to lose weight by reducing calorie intake, but it comes back to two important concepts - metabolism and hunger. Eating breakfast stokes the body's fires, so to speak. It gives the body a kick-start and gets its metabolic rate back up to speed after an overnight fast. The longer you leave it before eating breakfast, the more your body tries to conserve energy by lowering its metabolic rate. Eating regularly throughout the day (this should not be interpreted as grazing all day) ensures the metabolic rate stays up, and also helps prevent the build up of hunger, which could lead to overeating later on. So, if you are not currently having breakfast, now is a good time to start. If you do not feel hungry or are in a hurry, try something light or easy to eat on the run, like yoghurt or fruit. Also, try not to over eat or eat too late the night before, as this can blunt feelings of hunger in the morning. So make a new start to the day the breakfast way!

Yunsheng M, Bertone ER, Stanek EJ et al. Association between eating patterns and obesity in a free-living US adult population. Am J Epidemiol 2003; 158: 82-92.

For further nutrition reviews, we recommend Everybody Nutrition Research reviews