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Low Fat or Low Carbohydrate Diet?

Low fat? Low carbohydrate? High fibre? Low GI?


Selecting the appropriate eating pattern to lose weight and optimise health is a confusing business. Ever since the Atkins diet revolutionised dieting the path to being slim and healthy is no longer a simple case of cutting down on full fat dairy, butter and meat and eating more pasta, bread and rice instead. A new study suggests that low carbohydrate and low fat diets are equally effective; the old "eat less, exercise more" mantra may indeed be the deceptively simple key.


Weight loss Aids

Confused and frustrated by conflicting dietary advice many people turn to quick fixes- shakes, meal replacements or pills that promise rapid results. Most of these do not stand up to scientific scrutiny; they are short term fixes that can be very damaging and  may leave the dieter fatter than when they started out and finding it even harder to shift excess weight. In combination with a balanced diet and exercise conjugated linoleic acid and green coffee have both been found to successfully promote fat loss and lean mass gain.



Since the Atkins diet the pitfalls of low fat diets have begun to emerge. Low fat diets involve the substitution of fatty foods for carbohydrates and other low fat foods such as skimmed yogurt and milk; such a diet can be very low in essential nutrients, in particular essential fatty acids and fat soluble vitamins, and very high in both natural and refined sugars and artificial additives while not necessarily being lower in calories. The effect of high intakes of carbohydrates, in particular refined carbohydrates such as white rice and bread, on the activity of the hormone insulin, which is produced to lower levels of sugar in the blood and stimulate the storage of excess energy as fat, have since been found to be detrimental. As a result carbohydrates have developed the reputation fats once had.  So what then is the truth?


An analysis of the results of five trials, involving a total of 447 participants, and a recent 1-year trial involving 311 obese women have both suggested that a low-carbohydrate diet is a feasible alternative to a low-fat diet for weight loss and may have other favourable effects on health. Long term studies however are lacking.


The Study

Researchers randomly assigned 322 moderately obese subjects to one of three diets- low-fat, Mediterranean or low-carbohydrate- and instructed them to follow the diets for two years. The low-fat diet contained 30% of calories from fat, 10% of calories from saturated fat, and an intake of 300 mg of cholesterol per day. The participants consumed low-fat grains, vegetables, fruits, and legumes, and limited their consumption of additional fats and high-fat snacks; calorie intake was restricted to 1,500kcal per day for women and 1,800kcal per day for men. The Mediterranean diet was rich in vegetables and fish, but low in red meat; calorie intake was restricted, the main sources of added fat were olive oil and nuts. The low-carbohydrate diet provided 20 g of carbohydrates per day for the 2-month induction phase with a gradual increase to a maximum of 120 g per day to maintain the weight loss. The intakes of total calories, protein and fat were not limited.


272 subjects adhered to their dietary plans for two years. The mean weight loss was 2.9 kg for the low-fat group, 4.4 kg for the Mediterranean-diet group, and 4.7 kg for the low-carbohydrate group. The largest increase in HDL "good"cholesterol, particularly relative to total cholesterol, was seen in the low carbohydrate dieters; the low carb dieters also experienced a significant decrease in triglycerides (fat in the form found in the bloodstream) as compared to the low fat dieters. Among the 36 participants with diabetes, only those in the Mediterranean-diet group experienced a

decrease in fasting blood sugar levels; this change was significantly different from the increase in plasma glucose levels among participants with diabetes in the low-fat group.


Interestingly although the low carbohydrate diet was not calorie restricted there was no significant difference in energy intake between the three groups; the low carbohydrate dieters had a higher intake of total fat, saturated fat, cholesterol and protein. The amount of physical activity increased significantly in all groups during the course of the study.


Click here to access the full text of the study.


The results of this study suggest that while any eating pattern that involves a significant decrease in calorie intake can produce weight-loss, a balanced diet that emphasises high quality protein, a balanced fat intake from natural sources including fish, olive oil, meat and dairy and a moderate consumption of high fibre carbohydrates can produce more significant results and a more substantial improvement in health. Fat is essential; it helps keep us warm, protects our internal organs, forms part of brain structure, transports fat soluble vitamins, makes up the membrane surrounding cells that enable communication between cells and forms hormones. While high fat foods are also the highest in calories and an excess of saturated fat has been linked to elevated cholesterol levels, eating high amounts of fat from oily fish is linked to a reduced risk of heart disease. Similarly carbohydrates are a vital part of the diet-in particular they provide glucose absolutely required by the brain as it cannot obtain it from fat stores- but eating a diet largely composed of refined carbohydrates that have only relatively recently formed part of the human diet such as soft drinks is detrimental to health and encourages excess calorie consumption. 


When it comes to eating healthy, balance is key.  

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