In the past, high fat diets have been slammed for their ability to increase weight and effect our overall health. Although, diets which are high in fat are often high in saturated fats and trans fats, which have been continually linked to obesity and cardiovascular disease. But what about a diet which is high in healthy fats such polyunsaturated fats (PUFAs) and monounsaturated fats (MUFAs)? More recent systematic reviews have highlighted the ability of high healthy fat dietary patterns such as the Mediterranean diet, to support modest weight loss in centrally obese individuals . In addition to this, the Mediterranean diet has also been shown to reduce waist circumference among a Mediterranean population group [2,3,4], as well as also reporting significant declines in body weight after a 5-year follow up period .
What is a High Healthy Fat Diet?
A high healthy fat is simply what the name suggests – a dietary pattern which is high in healthy fats, MUFAs, PUFAs and omegas-3 and -6. One dietary pattern which is high in these properties is the Mediterranean diet.
To most, this seems like a bizarre concept. How does a high fat diet reduce or maintain weight? There appears to be an anti-inflammatory effect of the Mediterranean diet through the high consumption of healthy fats, and in particular, the consumption of MUFAs .
Let’s break down how this mechanism works:
• Poor diet (particularly high in saturated fats) + limited exercise = weight gain, and often increased weight around our abdomens, which is known as central obesity.
• Fat in our abdomen is stored as two main types of fat, the first being subcutaneous fat, which sits beneath our skin and the second being, visceral fat, which is metabolically active .
• Indeed, it is the increase of this metabolically active fat, termed visceral fat, which creates a pro-inflammatory environment, which is induced by the increase in inflammatory molecules such as C-reactive proteins, interleukin-6 and tumour necrosis factor alpha .
• Diets which are high in saturated fats and processed foods are high in pro-inflammatory properties – which also contribute to inflammation in the abdomen.
• However, the benefits of MUFAs appears to be linked with their substitution of saturated fats in the diets [6,7].
• Saturated fats appear to activate of two receptors: TLR-2 and TLR-4 and activate downstream pro-inflammatory signalling, which increase inflammation by ‘activating’ these pro-inflammatory molecules [8,9].
• Due to the anti-inflammatory nature of MUFAs, it appears that they down-regulate pro-inflammatory signalling and reduce the secretion of pro-inflammatory cytokines and markers from “fat molecules” otherwise known as adipocytes and therefore reduce inflammation [9-11,16].
Furthermore, research has identified that a traditional Mediterranean diet can reduce inflammation in centrally obese individuals, highlighting the diets strength in reducing abdominal adiposity [9-11]. A recent update of the PREDIMED study suggested that a Mediterranean diet supported modest weight loss across 5 years .
Another proposed mechanism, which also may result in a reduction to weight, is the effect that MUFAs have on the oxidation rate and thermic effect of food. Changes to these measurements could be explained by a higher post-prandial fat oxidation rate and higher thermic effect of following a high MUFA meal [12, 17-18]. It appears that certain types of fats are favourably oxidised such as oleic acid, which a component of olive oil, while others are favourably stored such as saturated fats [13,14]. Therefore, suggesting that a Mediterranean diet, which is high in MUFAs may have been oxidising and utilising this dietary fat for energy as opposed to storing them – which would lead to an increase in weight.
We know that diet plays a major role in reducing body weight, but we also need to consider the role of physical activity as an important factor. A study conducted by Fernandez and co-workers , reported significant changes to both the hypocaloric Mediterranean diet only-arm and the Mediterranean diet + physical activity-arm. However, the changes to waist circumference were significantly higher in the Mediterranean diet + physical activity arm. This result just highlights that the combination of a healthy diet and physical activity have the greatest effect on weight – but the role of a healthy dietary pattern alone, reported changes to these measurements.
Where to from here:
In conclusion, the Mediterranean diet may be a useful tool to reduce body weight, particularly if the Mediterranean diet is paired with exercise. A non-energy restricted Mediterranean diet appears to be unlikely to cause weight gain, which does help remove the taboo around healthy high fat diets causing weight gain. However, there needs to be further research in this field, particularly in a non-Mediterranean population base and a ‘healthy’ weight population, to determine whether the Mediterranean diet has similar effects.
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