There are scientific trials that have shown low carb-high protein diets provides more weight loss than high carb-low fat diets, but equally there are a number of studies that don’t show that effect. One study has shown that a low fat diet is better than a moderate fat diet, whilst others have shown that a moderate fat, Mediterranean style diet is superior to a low fat diet.

Whatever the diet, there is short term research out there to both support and disprove it. Now research published in the New England Journal of Medicine has examined the advantages of high fat, protein or carbohydrate diets over 2 years. Unlike other diet studies this one had a large number of participants (811), involved a high number of men (40%), and had good adherence to the diet by the participants (80% completed the 2 years study compared to normal diet studies where 40% drop out).

The participants were aged 30-70 years old with a BMI of 25-40. They were randomly assigned to one of four diets, with the percentage of energy from each food source being:

• Diet 1: 20% Fat; 15% Protein; 65% Carbohydrate
• Diet 2: 20% Fat; 25% Protein; 55% Carbohydrate
• Diet 3: 40% Fat; 15% Protein; 45% Carbohydrate
• Diet 4: 40% Fat; 25% Protein; 35% Carbohydrate

Each person was given a diet with a deficit of 750 calories a day as calculated from their resting energy expenditure and activity levels. Also 90 minutes of moderate exercise a week was prescribed.

Other goals of the diets were they should have

• 8% or less saturated fat,
• at least 20% fibre,
• 150mg or less of cholesterol per 1000kcal,
• carbohydrate foods with low glycemic index.

Typically weight loss is greatest 6-12months after starting a diet followed by a subsequent steady regain of weight. In this study at 6 months participants in each diet had lost an average of 6kg (7% body weight). The participants in each diet reported a reduction in calories of around 400kcal, although a mean weight loss of 6.5kg at 6 months corresponds to a reduced daily intake of approx 225kcal.

There are two common body shapes that develop when fat accumulates, apple shapes appear when fat collects in the abdominal area, this is termed upper body obesity (UBO). The other body shape is pear, when fat resides on the hips, which is known as lower body obesity (LBO).

Researchers from the Netherlands have investigated if the way the body deals with consumed fatty acids is different in men with upper or lower body obesity.  Previously research has shown that the chain length of dietary fatty acids is important in affecting fat absorption, fat metabolism and fat transportation around the body.

Medium chain triglycerides (MCT) are a type of dietary fatty acids which passively diffuse to the portal system (a system of blood vessels), without requiring modification or bile salts for digestion. Rich sources of MCTs include coconut oil and palm kernel oils. Some studies have shown MCTs can help the process of excess calorie burning and weight loss although almost half of the calories in your diet would have to come from MCTs themselves. 

Polyunsaturated fatty acids (PUFA) compared to MCTs are longer fatty acids which are absorbed into lymphatic system.  PUFA can be found in grain products or sea food. Beneficial PUFA include Omega-3 fatty acids found in fish, which reduce the risk of heart attacks and Omega -6 found in sunflower oil which can reduce the risk of cardiovascular disease.  However, high consumption of Omega 6 may increase the developmental risk of breast cancer in postmenopausal women or prostate cancer in men.

It has been suggested that within the body PUFA is disposed to the periphery (organs, muscles or subcutaneous fat) and MCT disposed more centrally. As MCT are often rapidly broken down than stored, a diet rich in MCT has been advised to people suffering from obesity problems

In the study published in this month’s Genes and Nutrition journal, researchers profiled adipose tissue biopsies from mildly obese men to investigate the effect of body fat distribution on the physiological response to two dietary fat interventions. Subjects with a BMI of 27-35 participated in the research.  Men with Waist to Hip Ratio (WHR) <1 were considered LBO and WHR>1 as UBO. As part of the trial they consumed a spread containing predominately either PUFA (71% long-chain fatty acids) or MCT (65% medium- chain fatty acids). Each day the subjects consumed 60g of the spread for two weeks.

The results showed a negative regulation of the metabolic pathways (lipid, carbohydrate and amino acid metabolism) in upper body obesity subjects when they consumed MCT compared to a PUFA diet. Despite previous recommendations that a  MCT based diet improves obesity traits, the findings from this study suggests a MCT diet in apple shaped people may have an adverse effect with increased inflammation and decreased energy metabolism in adipose tissue.

Dr Marijana Radonjic the papers author, reports that as there are different physiological characteristics of upper and lower body obesity, fat distribution is an important parameter to consider when selecting a personalized dietary regime.

Aerobic exercise is effective in improving our cardiorespiratory fitness whilst  improving the burning of fat and overall energy use. Weight training or resistance work acts as a stimulus to the muscularskeletal system to increase muscle size and strength. It is therefore recommended that a training routine combines both types of exercise as each has its own advantage. Normally aerobic or resistance exercises are performed in a single training session and if are combined aerobic exercise is often completed first as it is seen as a warm up of the muscle prior to resistance training.

A group of researchers from the College of New Jersey however wanted to examine the impact of resistance training prior to aerobic exercise. The study published in European Journal of Applied Physiology involved 11 males and 21 females who ate a moderate (50%) carbohydrate diet. Six static weight machines were chosen for the resistance exercises: Leg press, lat pull down, leg extension, seated row, shoulder press and chest press. For each subject their 8-RM was determined. This being the maximum amount of weight that could be lifted through a full range motion 8 times. Each subject completed each one of the following trials on different days

1. Aerobic exercise only (C) (cycle for 20mins at 50% maximum oxygen uptake (VO₂max))
2. High intensity resistance training (HI)  (3 sets of 8 reps at 90% of 8-RM) followed by aerobic exercise
3. Low  intensity resistance training (LO) (3 sets of 12 reps at 60% of 8-RM) followed by aerobic exercise

Throughout each aerobic activity the researchers looked at oxygen uptake and also the oxidisation of carbohydrate and fat. Oxidisation is when the fuel source ie, fat or carbohydrate, combines with oxygen to provide energy.  They found that fat oxidisation  and oxygen uptake was higher in the HI group than either LO or C in both males and females. Prof Kang, the paper’s author suggests that whilst fat oxidation following LO training was itself higher than aerobic exercise alone it is the intensity of the resistance exercise that is more important than the total volume of exercise completed.

Interestingly after the first five minutes of aerobic exercise they found no difference in carbohydrate oxidation rates. Prof Kang suggests that it appears in training that combines both aerobic and resistance exercises, performing a comparatively higher intensity resistance exercise first would boost the use of fat and energy during any subsequent aerobic activity.

He suggests that the metabolic effect of the resistance work is due to an increase in lipolytic hormones, which may have a short time before they revert back to their resting levels and that the aerobic exercise should ideally start within 5mins of resistance exercise, but after no more than 20mins.

So according to Prof Kang’s research if you really want to burn fat quicker get to the gym half an hour before your aerobics class or run and lift some weights.