The truth about fast food and getting fat

There is a widespread belief that eating fast food (eg hamburger, fries and Coke meals) is intrinsically bad for your health and is a sure path to obesity. This notion was copper- fastened in the public mind by Morgan Spurlock's 2004 documentary film Super Size Me. However, subsequent experience has shown that this simple message is wrong – growing fat is determined by excess calorie ingestion, not by the category of restaurant where the calorie ingestion occurs.

Morgan Spurlock tested the effect of intensive consumption of fast food by eating breakfast, lunch and dinner at McDonald's (the archetypal fast-food outlet) for 30 days, recording his experience on film. He ingested about 5,000 calories per day and took little exercise, confining himself to the average American activity of taking 5,000 steps per day (about two miles). At the start of his experiment, 188cm-tall Spurlock was in good shape. He weighed 84kg, was reasonably fit and had a blood cholesterol level of 170 mg per 100 ml blood (mg%). Over the 30 days he gained 11.1 kg in weight and his cholesterol level rose to 230 mg% – less than 200 mg% is "good", 200-239 mg% is "borderline high" and 240 mg% and above is "high".

Several days into his experiment, Spurlock reported feelings of depression that were lifted by eating McDonald’s food. His doctor described him as “addicted” to it. Spurlock reported reduced energy and libido levels and by day 21 he developed heart palpitations.

Spurlock's film made a big public impression and was nominated for an Academy Award as best documentary. Many people concluded that eating fast food is intrinsically bad for health, but this simple conclusion has been convincingly rebutted in the meantime.

The latest rebuttal comes from Iowan schoolteacher John Cisna, who ate exclusively at McDonald's for 90 days. He chose a diet giving a daily calorie intake of 2,000 calories and he followed US Federal guidelines for intake of protein, carbohydrate and fat. He also took a daily 45-minute brisk exercise walk. Cisna's typical diet was: breakfast – two egg white McMuffin Delights and a bowl of maple oatmeal in 1% milk; lunch – a salad; dinner – a McDonald's traditional value meal.

Cisna was in poor shape at the start of his experiment, weighing 127kg and with a blood cholesterol level of 249 mg% (high). Over the 90 days on the McDonald's diet he lost 16.8kg weight and his cholesterol dropped to 170mg%. In particular his LDL ("bad") cholesterol dropped from 173 mg% to 113 mg%. Cisna emphasises that he didn't achieve these results by eating only salads and drinking water. He also ate Big Macs, Quarter Pounders with Cheese, sundaes, ice cream, etc.

Little surprise
In hindsight there is little to surprise in either Spurlock's or Cisna's experiences. If you ingest 5,000 calories a day for 30 days (Spurlock) and take very little exercise you will pile on weight, whether you eat at McDonald's or at Ballymaloe. Cisna was very overweight before his experiment and taking no exercise, so, 90 days' ingesting 2,000 calories per day combined with daily exercise was bound to do him good. Cisna's and Spurlock's experiences combined simply confirm what rigorous scientific research has shown, namely that reduced-calorie diets, regardless of their composition, bring about significant weight loss when eaten on a sustained basis (FM Sacks and others, New England Journal of Medicine, Vol 360 No 9 pp857-873, February 26th, 2009). Fast food can make up a significant fraction of such a diet.

However, that said, it is difficult for the average person to eat healthily in fast-food outlets because the highlight offerings are usually high in fat (calorie dense) and salt (raises blood pressure). However, as Cisna showed, you can navigate the menu and choose nutritionally sensible meals, but you must exercise self-control. Don’t choose the enormous hamburger – choose the small basic burger. Don’t wash down your food with a bucket of Coke – buy the small Coke or a bottle of water – and so on.

Although neither Spurlock nor Cisna carried out rigorous scientific experiments, their studies do provide useful information. I conclude that it is unwise to demonise fast food but wise to eat it only very occasionally. At the end of the day, it all boils down to choice and self-control, something at which most of us do not excel. As Cisna says: “We all have choices. It’s our choices that make us fat, not McDonald’s.”

[ understandingscience.ucc.ie ]