Why Low-Fat Diets Aren’t Better For Weight Loss

Why Low-Fat Diets Aren’t Better For Weight Loss

If food is labelled low fat, it’s got to be better for weight loss, right? Wrong — it’s the total kilojoules that matter most for weight loss. Looking solely at fat content only gives you part of the picture.

Salad picture from Shutterstock

Back in the 1970s, few foods were specifically manufactured to be low in fat. If, on doctor’s orders, you had to follow a low-fat diet, a trip around the supermarket was fast — skim milk, lots of vegetables and fruit, cottage cheese, fresh fish, and that was about it. Needless, to say you lost weight and got bored very quickly.

In 1982, we got our first set of Australian Dietary Guidelines, recommending we “avoid eating too much fat”. After that, a few more low-fat products appeared on the supermarket shelves.

The second edition of the guidelines in 1992 called for us to “eat a diet low in fat, and in particular, low in saturated fat”. This was attributed to recognition that obesity had now become a problem in Australia.

Then, in the mid-1990s, guidelines for foods with low-fat and reduced-fat content claims on their labels appeared in the Code of Practice on Nutrient Claims. From this time we really started to see an increase in products making these claims.

If a food label claims a product is low in fat, it must contain only three grams of fat or less per 100 grams of product. If it says reduced fat, it must contain at least 25 per cent less fat than the usual version of this food.

The dietary guidelines were revised again in 2003 and the recommendations for lower total fat and saturated fat choices were embedded across a number of the guidelines, with a specific statement to “take care to limit saturated fat and moderate total fat intake”.

We have now been advised to reduce our fat intakes for over 30 years, and low-fat products flood our supermarkets and food courts. Sadly, however, our waistlines have continued to expand and our fat intakes have not reduced.

Something is clearly awry. Somewhere along the way, low fat has been misinterpreted to mean “eat more” because it is low in fat. So rather than linger over a sliver of sponge cake that would contain about 600 kilojoules (150 Calories), I can scoff a muffin the size of a small plate with as many as 2000 kilojoules (500 Calories), because the sign said low fat.

Just because a food is low in fat doesn’t mean it’s low in total kilojoules.

What Does The Evidence Say?

Food is made from macro-nutrients: protein, fats and carbohydrates. These each provide energy in the form of kilojoules. One gram of protein provides 17kJ, one gram of carbohydrate provides 16kJ and one gram of fat provides 37kJ. Fat has the highest kilojoules so you would think that following a diet low in fat should automatically mean you eat fewer kilojoules and lose weight. Not so.

My colleagues and I recently updated the adult weight-management guidelines for the Dietitians Association of Australia and reviewed the recent evidence comparing higher carbohydrate/lower fat diets for weight loss to higher fat/lower carbohydrate diets.

The good news was we found there were lots of studies, with a systematic review and seven recent randomised-controlled trials. Overall, when protein and energy intake were held constant across the two diets, both approaches were equally effective in achieving weight loss.

Back onto the Australian Dietary Guidlines, the latest draft says to “limit intake of foods and drinks containing saturated and trans fats and to include small amounts of foods that contain unsaturated fats.”

If you’re putting low-fat foods into your shopping trolley, it’s wise to stick to the ones that would have been around in your grandparent’s day. This means eating more vegetables, fruits and low-fat dairy products, plus whole grains, fish, or vegetarian sources of protein such as baked beans. It also means avoiding packaged and highly-processed low-fat foods.

If a low-fat diet is not palatable to you, you can still lose weight eating more fat, but you will need to be more aware of the kilojoule value of the foods you choose to eat.

The bottom line is that when it comes to weight loss, watch the total kilojoules, because it’s excess kilojoules rather than dietary fat that leads to weight gain.

Clare Collins is Professor in Nutrition and Dietetics at University of Newcastle. She is a fellow of the Dietitians Association of Australia who has published guidelines for dietitians for the mangement of overweight and obesity in adults. She receives fuding from the NHMRC and the ARC and has written books on weight loss for the general public

The ConversationThis article was originally published at The Conversation. Read the original article.


  • It surprises me that people still need to be taught that the recipe for being overweight pretty much boils down to “energy intake > energy expenditure” it doesn’t matter where the energy comes from (although some forms are more easily converted to fat in the body).

    The only way fat-free and low-fat diets work is the food tastes so bad that you don’t want to eat any more.

  • Agree, one of the manufacturers tricks is to put Low Fat on the label but pump it full of sugar. For example, it’s pretty hard to find mayonnaise without sugar in it, something that shouldn’t have any sugar in it. And one of the mayo’s that said Low Fat actually had more sugar than egg. The rules should be changed so they can’t use Low Fat unless there is under a certain amount of sugar as well. People are being tricked into thinking they are buying the healthy option.

    • People aren’t being tricked, you can’t blame food labelling for people misunderstanding it through their own ignorance. The onus is on them to learn and know what is healthy.
      And Low Fat labels are just that, low fat. It doesn’t and isn’t meant to encompass any other macro-nutrient.

      • The burden of responsibility goes both ways. If a company promotes it’s products as ‘low fat’ there is a very obvious implication that it is a generally healthy product also. This is the same as items marked ‘diet’, or ‘lite’, or ‘skinny’, in my opinion.

        So yes – caveat emptor – buyer beware – always holds, but simply conforming to the minimum legal requirement regarding food labeling may not always meet the minimum socially accepted requirements.

        Anyway – I’m off to buy a ‘meat’ pie for lunch…

  • My youngest had his first day in Kinder today. The teacher gave each of the kids a box of Weight Watchers Muesli Bars to take home as a recommendation of a good snack for kids.
    Keep in mind these are Weight Watchers Muesli Bars. . .
    28% Fat
    23% Sugar

  • So, does the kJ on food packaging include all the kJ from protein, fat, and carbs? Or, do we need to do the calculations manually when comparing 2 products?

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