Low Fat Diets Under the Spotlight

By Dietitian, Juliette Kellow BSc RD

The Atkins diet might have grabbed our attention with its promise that you can fill up on fatty foods while still losing weight. But despite its popularity with many slimmers, most health experts have stood their ground and said that if you want to lose weight – and keep your heart healthy – you’d be better off following a low-fat diet.

While low-fat diets might seem to have been around forever, in reality, they’ve only enjoyed fame for the past two decades. In 1983, the National Advisory Committee on Nutrition Education (NACNE) published a report outlining the links between diet and disease. For the first time ever, dietary targets were set to reduce the nation’s consumption of fat, saturates, sugar and salt, and to increase fibre intakes.

Then in 1984, came another landmark report that focussed specifically on diet and cardiovascular disease. Published by the Committee on Medical Aspects of Food Policy (COMA) – the government body responsible for making nutritional recommendations – this report gave guidelines for reducing the consumption of fat and saturates to help prevent cardiovascular disease.

In the next decade, an abundance of new research linking diet with heart health became available and in 1994, a new COMA report on diet and cardiovascular disease was published. This time recommendations on fat were extended to include monounsaturated fats, polyunsaturated fats and trans fatty acids.

But while these early reports focussed on slashing fat intakes to reduce the risk of heart disease, many health experts were also starting to recommend a reduction in fat to help people lose weight. And on the back of this, came a whole host of popular low-fat diets ranging from Rosemary Conley’s realistic Hip and Thigh Diet to the more extreme Pritikin Diet. Best of all, most of these low-fat diets seemed to work if you followed them properly. Even today, most health experts are in agreement that a low-fat diet combined with a high-fibre intake is the best way to lose weight – and keep it off!

So how does a low-fat diet help you lose weight?

Regardless of the diet you follow, to lose weight you have to lower your calorie intake sufficiently to create an energy deficit so that your body has to start using its fat stores to supply it with the extra calories it needs to function properly.

Of all the nutrients, fat is the most energy dense ie. it contains the most calories. Each gram of fat contains 9 calories whereas protein provides 4 calories per gram and carbohydrate, just 3.75 calories per gram. Only alcohol comes close to fat with 7 calories per gram. This means one of the easiest ways to cut calories is to reduce the amount of fat in your diet (together with reducing alcohol).

How much fat should I have each day then?

In the UK, most of us get around 35 to 40 percent of our calories from fat. But for good heath, national guidelines recommend that no more than a third of our calories should come from this nutrient.

When it comes to losing weight, however, much research has looked at the benefits of further restricting fat intake. There’s good evidence to suggest that a moderate fat restriction, where fat provides around 20 to 30 percent of calories is more effective than a very low-fat intake, where fat provides fewer than 20 percent of calories. This is because diets that are extremely low in fat tend to be too restrictive and boring for most people, with the result they give up easily. Furthermore, research shows a moderately low-fat diet, where 20 to 30 percent of calories come from fat, is more likely to keep the weight off in the long term.

That’s why Weight Loss Resources (WLR) recommends a moderate fat restriction where 25 to 30 percent of calories come from fat.

But exactly how many grams of fat should I have each day?

The amount of fat most people should have will depend on their calorie intake and the degree of restriction they want to follow. The table below gives rough guidelines. However, it’s not essential to stick rigidly to the suggested fat intake every single day.

Enter Audrey Eyton’s world-famous F-plan diet! In May 1982, copies of The F-Plan Diet went on sale, and even today it remains popular. Ultimately, it promoted a high-fibre, low-fat, calorie-controlled eating plan – in fact, pretty much what nutrition experts still recommend today if you want to lose weight.

  Recommended intake of fat grams where…
Daily calorie restriction …20% of calories come from fat …25% of calories come from fat …30% of calories come from fat
1,100 24 31 37
1,200 27 33 40
1,300 29 36 43
1,400 31 39 47
1,500 33 42 50
1,600 36 44 53
1,700 38 47 57
1,800 40 50 60
1,900 42 53 63
2,000 44 56 67
2,100 47 58 70
2,200 49 61 73

How do I work out the percentage of calories that come from fat?

Fortunately, WLR does this for you – your nutrition profile will provide details of the percentage of calories you’ve had from all the main nutrients each day. But if you want to have a go yourself, you’ll need to know the total amount of fat and calories you’ve had in a day – and arm yourself with a calculator! Here’s how to do it…

  1. To calculate the number of calories that have come from fat, multiply the grams of fat you’ve had in a day by 9 (each gram of fat provides 9 calories).
  2. Divide this value by the number of calories you’ve had in the day.
  3. Multiply this by 100 to give you the percentage of calories that have come from fat.

For example, if you’ve had a daily intake of 35g of fat and 1,250 calories, the calculation is as follows: 35 x 9 = 315 ÷ 1,250 = 0.25 x 100 = 25. This means 25 percent of your calories have come from fat.

Wouldn’t it be better to have a completely fat-free diet to lose weight?

It’s virtually impossible to have a fat-free diet as most foods, even fruit and veg, provide small amounts of fat. But that aside, we actually need some fat in our diets. Certain components of fat are essential parts of our body cells and are needed to make hormones. Fat also helps to insulate our body and small amounts around the major organs have a protective effect. Several vitamins (vitamins A, D, E and K) are also fat-soluble and tend to be found in foods with a high fat content. A very low-fat diet may mean that intakes of these vitamins are often extremely low, too.

Furthermore, two fatty acids – linoleic acid (omega-6s) and linolenic acid (omega-3s) – can’t be made by the body and so must be supplied in the diet. These fatty acids, known as essential fatty acids, are needed in small amounts for growth, healthy skin and to protect against certain diseases. Vegetable, nut and seed oils tend to be good sources of omega-6 fats, while oily fish is a great source of omega-3 fats, important for helping to prevent blood clots.

There’s even some evidence to suggest that omega-3 fats can aid weight loss, by helping to keep blood sugar levels steady. This means cravings are less likely to occur with the result that you won’t want to constantly snack in an effort to beat the munchies.

That aside, extremely low-fat diets are not very palatable so you’re far more likely to give up your diet and go back to the same eating habits that made you gain weight in the first place.

When it comes to losing weight, does it matter what type of fat I eat?

Ultimately, all fat contains 9 calories per gram so if you want to lose weight, it’s important to cut down on the total amount that you eat. But to keep your heart healthy, it’s also important to make sure you’re eating the right types of fat.

There are three main types of fat in food – saturates, monounsaturates and polyunsaturates. Most foods contain a mixture of these, but are generally classified according to the type of fat found in the largest amount. Here’s the lowdown…

Saturated Fats

A diet high in saturates increases levels of LDL or ‘bad’ cholesterol in the blood, and this is one of the risk factors for heart disease. Therefore, regardless of whether you’re trying to lose weight, it’s important for everyone to eat fewer foods that are rich sources of saturates, such as fatty meats, full-fat dairy products, butter, lard, cream, cheese and many processed and takeaway foods.

Polyunsaturated Fats

Research shows that polyunsaturates can lower LDL or ‘bad’ cholesterol but have no effect on HDL or ‘good’ cholesterol, the type that protects against heart disease. The polyunsaturated group of fats contains omega 6’s and omega 3’s (see above). Good sources of polyunsaturates include pure vegetable oils and spreads such as sunflower, corn, grapeseed and soya oils and margarines, nuts, seeds, some vegetables and oily fish such as mackerel, sardines, salmon and fresh tuna.

Monounsaturated fats

These have double whammy effect on cholesterol levels. As well as lowering LDL cholesterol, they also raise HDL cholesterol. Good sources include olive oil, avocados, nuts and seeds.

The bottom line: to lose weight you need to cut down on the total amount of fat you have in your diet as all fat is high in calories, irrespective of the type. But to keep your heart healthy, you should also swap as many foods that are rich in saturates for unsaturates.

What are trans fats and are they bad for me?

Trans fats are created when pure vegetable oils are processed. During manufacturing, these liquid oils have hydrogen bubbled through them in a process called hydrogenation to improve their texture, flavour and shelf life. The resulting product is a more solid fat, called hydrogenated fat or hydrogenated vegetable oil, which goes on to be used as an ingredient in many processed foods. Unfortunately, a side effect of this manufacturing process is the creation of trans fats, which are thought to be just as harmful to health as saturates.

Unfortunately, most products don’t provide details about their trans fat content on the label – instead you need to look at the ingredients list. If a food contains hydrogenated vegetable fat or oil, it will almost certainly contain trans fats and so you should limit the amount you eat. The higher up the list the ingredient appears, the more trans fats the product will contain. In general though, trans fats are found in cakes, biscuits, margarines, takeaways, pastry, pies and fried foods – the very foods you should be eating less of anyway if you want to lose weight!

I’m confused about oily fish. It’s high in calories and fat so does this mean I should avoid it if I want to lose weight?

Salmon, mackerel, sardines, trout, fresh tuna and other oily fish are much higher in calories and fat than white fish or shellfish. But they also contain two types of healthy omega-3 fats – eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA) – both of which are essential for good health.

To start with, omega-3s make blood less sticky, preventing blood clots from forming that can block blood vessels causing a heart attack or stroke. Meanwhile, studies have found that people who eat more omega-3 fats have lower blood pressure, and therefore are at less risk of stoke.

Research has also shown that omega-3s can help to improve autoimmune diseases such as rheumatoid arthritis and lupus. Both EPA and DHA are converted into natural anti-inflammatory substances called prostaglandins, which reduce inflammation and the pain associated with them. Meanwhile, further research shows omega-3 fats are also important for the development of brain cells and may help to boost brain power.

Current healthy eating guidelines recommend that we eat two portions of fish a week, one of which is oily. So rather than avoiding salmon, sardines, mackerel, trout or fresh tuna, simply eat it at least once a week and work the calories into your allowance.

What about nuts and avocado?

The same goes for nuts and avocado. These foods are also high in fat and therefore calories, but they’re packed with heart-healthy monounsaturated fats and so can be eaten as part of a healthy diet. You just need to remember to work the calories into your allowance.

Is there a simple way to tell if a food is low in fat?

Looking at food labels is one of the easiest ways to identify whether or not a food contains a little or a lot of fat. Legally, any food that claims to be ‘fat free’ should have less than 0.15g fat per 100g, whereas foods that claim to be ‘low fat’ should contain less than 3g fat per 100g. As a general rule, more than 20g fat per 100g is a lot.

Be aware that ‘reduced-fat’ products aren’t automatically low in fat. On food labels, the term ‘reduced-fat’ simply means the food must contain 25 percent less fat than the equivalent standard product. For example, a reduced-fat Cheddar may still contain around 26g fat per 100g – and that’s a lot!

Similarly, beware of products labelled ‘light’ or ‘lite’. There’s no legal definition for these terms so manufacturers often use them as they wish, for example, to convey a products texture or to give the impression that it has less fat or calories when this isn’t actually the case.

Finally, be warned that ‘low-fat’ doesn’t automatically mean that a product is low in calories, too. Many low-fat products can still be packed with calories. For example, a healthy-sounding low-fat blueberry muffin might contain very little fat, but can pack in more than 500 calories – almost half the recommended calorie content for some slimmers!

The bottom line: even if you’re following a low-fat diet, you may still need to check the calorie content of certain foods.

Are there any cons to low-fat diets?

Not really, providing you follow a moderate fat restriction, rather than severely trying to limit your fat intake. One thing to watch out for though is the huge number of low-fat products that are now readily available. Many of these foods including snack bars, biscuits, cakes and ice cream, contain loads of sugar and so are still very high in calories and not great contenders for a healthy diet. Before filling your trolley with them, glance at the calorie content first to check that a normal sized serving won’t blow your daily calorie allowance.

Juliette’s verdict

Like most nutrition experts, I’m a fan of low-fat diets. As well as helping to lower the risk of heart disease, they have an important part to play in terms of helping people to lose weight and keep it off. But it’s also important to remember that fat is not the only culprit in the fight against obesity. Ultimately, the only way to lose weight is to take in fewer calories than your body needs and while low-fat and fat-free foods can help you do this, you may still need to check out their calorie content or limit serving sizes of naturally low-fat foods such as pasta, rice, potatoes, bread and breakfast cereals.

10 easy ways to eat less fat

  1. Eat fewer fried foods – ditch frying and grill, boil, bake, poach, steam or dry roast instead.
  2. Don’t add butter, lard, margarine, dripping or oil to food during preparation and cooking.
  3. Use spreads sparingly. Butter and margarine both contain the same amount of calories and fat. Only low-fat spreads contain less.
  4. Choose boiled or jacket potatoes instead of chips or roasties.
  5. Trim all visible fat from meat and remove the skin from chicken before cooking, especially if those are the bits you can’t resist!
  6. Eat fewer fatty meat products such as sausages, burgers, pies and pasties. If you want to indulge, go for low-fat varieties if available and avoid frying them.
  7. Use semi-skimmed or skimmed milk instead of whole milk.
  8. Eat low-fat or reduced-fat varieties of cheese such as reduced-fat Cheddar, reduced-fat mozzarella, goat’s cheese or cottage cheese.
  9. Eat fewer high-fat foods such as crisps, chocolates, cakes, pastry products, biscuits, pizza and takeaways.
  10. Use low-fat natural yoghurt, fat-free fromage frais or reduced-fat fromage frais as a topping for puddings or in sauces instead of cream.

Can eating fat actually make you fat?

Research shows this may well be the case! Apart from containing more than twice as many calories as carbohydrate or protein, the fat in food is actually very good at becoming body fat compared with these other nutrients. This is because dietary fat uses only a tiny amount of calories in an effort to become body fat, whereas carbohydrate, for example, uses around 25 percent of its calories to turn itself into body fat. This means an extra 100 calories from fat will result in a greater gain in body fat than an extra 100 calories from carbs.

Added to this, high-fat diets are also very palatable, especially when combined with sugar or salt such as crisps, cakes, biscuits, puddings and chocolate. And because these foods taste so good, this means we’re far more likely to eat excessive amounts of them. In fact, research shows that high-fat foods can make us eat excessively before the brain recognises that we’re full. That’s not to say that low-fat meals can’t satisfy us though. Research also shows that you can remove a considerable amount of fat, and therefore calories, from meals without most people even noticing.

Follow A Low Fat Diet

You can follow a low fat diet using the food diary and database tools in Weight Loss Resources. Try it free for 24 hours.

Take our FREE trial »

Lose a Stone for Christmas Challenge

If you enjoyed this article, try our newsletter. It's free.

Receive the latest on what works for weight loss straight to your inbox. We won't share your email address. Privacy policy