Diet dilemmas

A patient once told me she couldn’t lose weight. She’d been on multiple diets over the previous years and had retained elements of each in her quest for a slimmer figure. It didn’t work...

Her story deftly illustrates the morass of half-baked fallacy and mumbo-jumbo that exists in this area. To help you avoid the same pitfalls here is my analysis of some of the diets currently doing the rounds — some have positive benefits, but most won’t yield successful long-term weight loss — although may make your wallet thinner.

1 LOW CARB DIETS (e.g. the Dukan Diet, the Atkins Diet, the South Beach Diet)

These are all low-carb, high-protein diets that encourage a high intake of lean meat, fish and poultry, but which limit fruit, vegetables and wholegrains. They achieve weight loss, but do this by depriving the brain of its preferred fuel (carbohydrate). Unfortunately, the brain is very fussy about the energy source it uses, so without carbohydrate, the body has to break down fat in a non-physiological way called ketogenesis to provide an alternative brain fuel. Ketogenesis is usually only seen in starvation, and gives rise to a characteristic, acetone-like smell on the breath. While the long-term health impact of this “fuel change” is unknown, these diets are inherently low in many important vitamins and minerals. They also pose a potential risk to kidney, heart and skeletal health, because of their very high protein, fat and phosphate contents.

Rating: 4/10

2 THE GLYCAEMIC INDEX (GI) DIET

This diet is based on the avoidance of insulin spikes which occur in response to sugary foods, sugary drinks and other quickly absorbed carbs. While insulin’s main job in the body is to store away blood sugar, it also builds fat tissue, especially around the tummy. So in theory low GI foods like porridge, wholemeal bread, pasta, raw carrots, cabbage, apples and milk, mean less insulin, and this means less fat building. In addition, most low GI foods (e.g. brown rice, broccoli, peaches, most beans) are also low in fat, salt and calories, and high in vitamins and minerals, so they confer multiple advantages. Now for the tricky part: GI tends to rise when a starchy food like potato is cooked and served warm due to a process called gelatinisation which makes its carbohydrate content more readily digested and absorbed. As the starchy food cools its carbohydrate begins to re-crystallise into resistant starch, a much less digestible form, thereby reducing its GI. To add further complexity and confusion, the moisture content, ripeness, and simultaneous consumption of other foods can also influence the GI of any given food. Furthermore, even low GI starchy foods can cause weight gain if taken in excess.

Rating: 7/10

3 THE ALKALINE DIET

This diet advocates taking foods which are alkaline in nature (in reality, virtually all foods are acidic), on the basis that these will have a favourable effect on the pH of blood. In fact, the body strenuously maintains blood pH within a very tight range, by a number of mechanisms and for very good reason. In short, there’s zero evidence to support any of this diet’s claimed benefits.

Rating: 0/10

4 THE DASH DIET

The inventors of DASH were originally looking for a diet to lower blood pressure, but found their regimen also had weight loss and other health benefits. It’s really simple to implement — four-plus servings of vegetables/salad, four-plus portions of fruit and three to four servings of low fat dairy (milk, yoghurt) daily — possibly the best of the lot.

Rating: 9/10

5 THE PALEO DIET

Based on our ancestral diet, this regime advocates a high intake of lean meat, chicken, fish and eggs, along with plenty of fruit, vegetables and nuts. Because it avoids agriculturally-produced foods, however, dairy, wholegrains and legumes are all excluded. The resulting fibre, calcium, vitamin D and riboflavin deficiencies can seriously impair health as we age — an issue our shorter-lived caveman forebears didn’t have to worry about.

Rating: 5.5/10

*Dr Daniel McCartney is a lecturer in nutrition and dietetics at DIT.


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