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Diets that do and diets that don’t: Part 3 – The Blood Group Diet

By Tamzyn Murphy

BSc Med(Hons) Human Nutrition and Dietetics, RD

 

Eat right for your type, by naturopathic doctor Peter D’Adamo, was first published almost 20 years ago, but it’s more popular than ever. It advises people to eat certain foods and avoid others based on their blood type – O, A, B or AB. According to D’Adamo, your blood type determines how your body digests lectins (anti-nutrient proteins found in certain foods). Apparently, eating lectins that are incompatible with your blood type causes a host of adverse health effects, from bloating and inflammation to weight gain. Allegedly, your blood type even determines what exercise suits you best.

 

Foods are categorised as ‘highly beneficial’ (with medicinal effects), ‘neutral’ (acting as a food) or ‘avoid’ (toxic) for each blood type. O (“for old” – humanity’s oldest blood line) types are told to follow a meat-based diet and vigorous exercise programme.  Type A (for “agrarian”) should eat vegetarian food and exercise gently. B types are thought to have nomadic genes and digestive systems that can tolerate many foods, except, amongst other things, wheat, corn and lentils. Bs should exercise moderately. D’Adamo says the “modern” AB blood type has a sensitive digestive tract and should avoid meat and poultry but can enjoy seafood, tofu, dairy, and most fresh produce. ABs should do calming exercises.

 

People probably love this diet because it sounds scientific; but nothing could be further from the truth. There is absolutely no evidence that some foods or exercises are good for people of one blood type and “dangerous” for another. It appears that D’Adamo has randomly bestowed fictional characteristics upon people of different blood types and thumb-sucked foods to put on his ‘beneficial’ and ‘avoid’ lists. If the diet has worked for you it’s probably because all blood types are encouraged to eat real, whole and natural foods in place of processed, sugary and fatty choices, and exercise is always recommended. These are prudent health recommendations that’ll work for anybody. Also each of the four diets loosely resembles a diet that has been shown to have weight loss benefits: The O diet’s a variation on the typical high protein, low carb diet; A’s vegetarian; B’s somewhat similar to the Mediterranean and low GI/GL diets and AB is Pescatarian. In my opinion, the blood type diet’s a perfect example of a fad diet that profits from people’s desperation. If it works, it’s not for the reasons you think.

 

References

[i] WebMD. The eat right for your blood type diet. Sep 2013

[ii] Eat right for your type. www.dadamo.com. Sep 2013

Diets that do and diets that don’t: Part 1 – The New Atkins Diet

By Tamzyn Murphy

BSc Med(Hons) Human Nutrition and Dietetics, RD

 

People across the globe are getting fat and desperate – a profitable situation for those peddling fad diets. Obviously conventional nutritional wisdom has failed us – eating fewer calories (particularly less fat) and burning more by exercising doesn’t cut through the flab. It appears that our will-power just isn’t strong enough to overcome the hunger that goes with this kind of advice. Authorities’ recommend that we base our eating on carbohydrate-filled food, with less than 30% of calories from fat and about 15-20% from protein. Much of these carbs come from refined starches and sugar, making our insulin levels skyrocket, which puts our bodies into fat-storage mode and makes us even hungrier. But before that sends you running into the arms of the latest diet, make sure you know which ones work and which are doomed to failure.

 

New Atkins Diet[i]

Atkins is a low carb diet – one of the stricter versions. You shouldn’t be hungry on this diet though and calories aren’t restricted. Most people think low carb diets are high in protein and low in fat. Thankfully this isn’t usually the case – fat keeps hunger at bay and the right types promote good health; while excessive protein could be dangerous. Low carb diets are typically high in fat (60% or more) and moderate in protein (about 25%). The aim is to keep insulin levels low by restricting carbs, thereby reducing hunger and fat-storage, and retraining the metabolism to burn fat instead of carbs.  They’re great for weight loss. And recent evidence indicates they may also reduce heart disease, diabetes and metabolic syndrome risk.[ii] They’re particularly beneficial for those with insulin resistance or pre-diabetes.[iii]

There are four phases to the New Atkins diet – an updated version of Atkins. Phase 1 is really strict, allowing only 20g of carbs a day – mainly from low carb veggies. As you move through the phases you gradually increase the amount of carbs you’re allowed according to the “Carb Ladder” – adding nuts, seeds, low carb fruits, certain dairy products and some legumes. During this process you’re supposed to learn what your individual carbohydrate tipping point is – eat less carbs and you lose weight, more and you gain weight. By the end you should have lost all of your excess weight and know how to make this diet a permanent lifestyle fixture to maintain your weight and optimise health.

Critics claim the high fat content, particularly saturated fat, of low carb diets is bad for heart health but recent evidence refutes this.[iv] Others worry that excessive protein puts strain on the kidneys and leaches calcium from the bones, but the protein content of these diets isn’t typically excessive and there’s no evidence that it negatively impacts on kidney[v] or bone health.[vi] Where casual Atkins dabblers go wrong is they use it as an excuse to pass up on vegetables, gorge in processed food and deep fry everything.

 

References

[i] New Atkins. 2011 

[ii] Azadbakht L, Izadi V, et al. Effect of a High Protein Weight Loss Diet on Weight, High-Sensitivity C-Reactive Protein, and Cardiovascular Riskamong Overweight and Obese Women: A Parallel Clinical Trial. Int J Endocrinol. 2013;2013:971724. Published online: Aug 2013 

and

Noakes TD, Windt J. Evidence that supports the prescription of low-carbohydrate high-fat diets: a narrative review. Br J Sports Med 2017;51:133-139 

[iii] Feinman RD, Pogozelski WK, et al. Dietary carbohydrate restriction as the first approach in diabetes management: Critical review and evidence base. Nutrition 2015;31:1-13

[iv] Siri-Tarino PW, Sun Q, et al. Saturated fat, carbohydrate, and cardiovascular disease. Am J Clin Nutr 2010;91:502–9

and

Harcombe Z, Baker JS, et al. Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: a systematic review and meta-analysis. Open Heart 2015;2:e000196.

[v] Brinkworth GD, Buckley JD, et al. Renal function following long-term weight loss in individuals with abdominal obesity on a very-low-carbohydratediet vs high-carbohydrate diet. J Am Diet Assoc. 2010 Apr;110(4):633-8 

[vi] Farnsworth E, Luscombe ND, et al. Effect of a high-protein, energy-restricted diet on body composition, glycemic control, and lipid concentrations in overweight and obese hyperinsulinemic men and women.