1. A word from research dietician Dr. Berber Vlieg-Boerstra

Peanuts and tree nuts are common causes of food allergy and affect around 1.5% of all children (1). Allergies to peanut and nuts are associated with severe or even fatal reactions. Fortunately, not all patients with peanut and nut allergy risk severe reactions, as about one-third of these patients display only mild reactions (2), and in other patients sensitized to birch pollen the food allergy may be limited to oral allergy syndrome caused by hazelnuts and peanuts.

Peanut allergy may resolve in approximately 20% and tree nut allergy in 10% of patients respectively (3), and even resolution of anaphylaxis has been described (4). However, in most patients, peanut and nut allergy will not disappear, and for these patients the only proven safe and effective management of any peanut and nut allergy is complete avoidance.

Diagnosis of peanut and tree nut free diet

Until now no therapy for food allergy has been available other than the avoidance of the implicated allergenic food. Usually, physicians and dieticians are involved in the dietary management of food allergy. Clinical history, skin prick tests and determination of specific immunoglobulin E (IgE) are helpful in diagnosing peanut and nut allergy. One of the major pitfalls in the diagnosis of food allergy is that sensitization to food may occur without clinical symptoms. This means that the patient is sensitized to the food in question, but can consume the food without displaying any symptoms. Therefore, dietary exclusion of peanuts and nuts needs to be followed by reintroduction, either by oral food challenge or in a (re)introduction plan at home (5).

In general, patients with a positive history of immediate symptoms should be food challenged under medical supervision and should not undergo reintroduction at home. This also applies to the following categories of patient: those sensitized to peanuts or tree nuts with risk factors for severe reactions, such as the coexistence of asthma or severe atopic dermatitis or rhinitis; adolescence or young adult age; those who have excluded peanuts or nuts from the diet for a prolonged period of time; and those located at a great distance from emergency medical care should not undergo (re)introduction at home.

(Re)introduction at home

The dietician can be helpful in designing introduction schedules using incremental amounts of the allergenic food. This is relevant, since research has shown that in the absence of instructions for peanuts dosage parents would administer a median of at least 25 times higher (150 mg) than the first dose of the introduction schedule, and for nuts at least 8 times higher (6).

Caution necessary for the introduction of peanuts and tree nuts into the diet

The advice frequently given to patients by health care professionals who are not knowledgeable in the field of food allergy to “introduce peanut and nuts carefully into the diet” is bad advice. For patients who do react during (re)introduction more severely than expected, such advice could lead to severe reactions. It is important to give patients clear guidance how to introduce the peanuts or nuts. Recently, the results of successful oral immunotherapy (OIT) in severe peanut allergy have been published by Clark et al. (7). The study involved administering increasing amounts of peanut in four peanut allergic children in a clinical setting. Although these results are encouraging for future therapeutic possibilities for peanut allergy, oral immunotherapy is still at an experimental phase, and the maintenance of tolerance needs further evaluation.

Sources:
1) Grundy J., Matthews S., Bateman B., Dean T. and Arshad S.H. Rising prevalence of allergy to peanut in children: Data from 2 sequential cohorts. J Allergy Clin Immunol 2002; 110: 784-9.
2) Ewan P.W. and Clark A.T. Long-term prospective observational study of patients with peanut and nut allergy after participation in a management plan. Lancet 2001; 357: 111-15.
3) Fleischer D.M., Conover-Walker M.K., Christie L., Burks A.W. and Rood R.A. The natural progression of peanut allergy: Resolution and the possibility of recurrence. J Allergy Clin Immunol 2003; 112: 183-9.
4) Vlieg-Boerstra B.J., Duiverman E.J., van der Heide S., Bijleveld C.M.A., Kukler J. and Dubois A.E.J. Should children with a history of anaphylaxis to foods undergo challenge testing? Clin Exp Allergy 2008; 38: 1935-42.
5) Venter C., Vlieg-Boerstra B.J. and Carling A. The diagnosis of food hypersensitivity. In Skypala I, Venter C (editors): Food hypersensitivity. Diagnosing and managing food allergies and intolerance. Wiley-Blackwell. 2009.
6) Vlieg-Boerstra B.J., Dubois A.E.J., van der Heide S., Bijleveld S.M.A., Wolt-Plompen S.A.A., Oude Elberink J.N.G., Kukler J., Venter C., Jansen D.F. and Duiverman E.J. Ready-to-use introduction schedules for first exposure to major allergenic foods in children at home. Allergy 2008; 63: 903-9.
7) Clark A.T., Islam S., King Y., Deighton J., Anagnostou K. and Ewan P.W. Successful oral tolerance induction in severe peanut allergy. Allergy 2009; 2009 Feb 17. [Epub ahead of print]

2. The antioxidant content of nuts might play a role in the prevention of chronic diseases

The consumption of nuts has been linked to a decreased risk of cardiovascular diseases in several large epidemiological studies. Most studies look at the favourable fat content of nuts to account for the positive changes in blood lipid profiles. However, the overall reduction of the risk of cardiovascular diseases through frequent nut consumption is greater than can be accounted for by changes in the blood lipid profile alone. Nuts also contain other nutrients that might contribute to lowering cardiovascular risk, such as polyphenols, including flavonoids. However, little is known about the content, profile and effect in humans of these antioxidative nutrients in nuts.

Nuts contain a lot of antioxidants

A recent in vitro study by Yang et al. showed that nuts contain a large amount of phenols, polyphenols and flavonoids, which are known to have a high antioxidant capacity. This was especially true for walnuts and pecans. It was found that the higher the total phenolic content, the higher the antioxidant activity observed in the specific nut variety. Due to the increase of antioxidant capacity, the cell proliferation in human liver tissue drastically declined, which could have a potential inhibiting effect on tumour formation.

Increased antioxidant activity in humans

Another recent in vivo study by Torabian et al. gives us more insight into the bioavailability of these different phenolic compounds in nuts and their actual antioxidant activity in humans. Thirteen healthy adults participated in this randomized, crossover study to investigate the acute effect of ingested almonds and walnuts on total plasma polyphenols content, antioxidant capacity and lipid peroxidation. The participants consumed either an almond smoothie, walnut smoothie or control smoothie for breakfast. There was a one-week wash-out period between the treatments. Blood samples were taken at 30, 90, 150, and 210 minutes after consumption.

An increase of total plasma polyphenols and total antioxidant capacity was already seen 30 minutes after consumption of the smoothie enriched with nuts. The values peaked at 90 minutes. When consuming the smoothie with walnuts the total plasma polyphenol value was much higher compared to the smoothie with almonds. However, the antioxidant capacity was greater following the almond meal. This can be partly explained by the fact that almonds are a better source of the antioxidant vitamin E.

Nut consumption for a healthy heart

Reductions in lipid peroxidation products were observed after consumption of nut smoothies. Lipid peroxidation products are highly reactive and might cause damage to the tissues. This implies that the antioxidant capacity of nuts may account for the cardiovascular risk reduction observed when nuts are consumed frequently. However, although the study investigated the effect of polyphenols, other beneficial nutrients in nuts could also have played a role in the effects observed. Therefore, it is possible that the measured effect is not only due to the phenolic content. Altogether, the authors concluded that the findings provide further support to the existing recommendations of the American Heart Association for the inclusion of at least 28 to 56 g of nuts daily as part of a healthy diet for a healthy heart.

Sources:
1) Yang. J., Liu R.H. and Halim L. Antioxidant and antiproliferative activities of common edible nut seeds. Food Science and Technology 2009; 42: 1-8.
2) Torabian S., Haddad E., Rajaram S., Banta J. and Sabaté J. Acute effect of nut consumption on plasma total polyphenols, antioxidant capacity and lipid peroxidation. Journal of Human Nutrition and Dietetics 2009; 22: 64-71.

3. Oral immunotherapy: a new technique to induce peanut tolerance

Peanut allergy affects 2% of the children in the UK, and this rarely resolves during their lifetime. Clark et al. tested oral immunotherapy on four male children with severe peanut allergy and concluded that immunotherapy is an effective treatment to induce peanut tolerance at a very young age.

The oral immunotherapy

To confirm clinical peanut allergy and define the amount of protein required to cause an allergic reaction, the four children (9-13 yrs) received either a placebo or active (peanut flour) peanut protein in differing doses 1, 5, 25, 50, 75, and 100 mg prior to the study. The starting study doses were chosen based on this pre-test. After having taken a higher dose for the first time, the subjects were observed for 2 hours in the clinic. If this went well, then this peanut flour dose was taken daily at home for 2 weeks followed by further increase in the dose. The doses were doubled at each step to a maximum of 800 mg of peanut protein/day (1600 mg flour).

The post-intervention challenge

Six weeks after the final dosing, the subjects underwent an open post-intervention challenge to eat 10-12 whole peanuts, to find out what the highest tolerated dose was. This dose was compared to the initial highest dose prior to the study. Since the achieved tolerance could have been lost if the subjects had stopped at this stage, they continued to take 800 mg of peanut protein per day, this being in the form of flour, butter or whole roasted peanuts. All subjects tolerated the intervention of this increased dosage to a maximum of 800 mg without any reported severe reactions, and continued to tolerate this dosage for 6 weeks.

Induced tolerance to peanuts

After the oral immunotherapy all subjects were able to eat 10-12 whole peanuts without any allergic response. This dose was much greater than the subjects could tolerate before the treatment (49- to 478-fold), and more than is likely to be encountered during accidental ingestion. According to the researchers, follow-up studies are necessary to determine the duration and frequency of the therapy in order to induce long-term tolerance.

Source:
7) Clark A.T., Islam S., King Y., Deighton J., Anagnostou K. and Ewan P.W. Successful oral tolerance induction in severe peanut allergy. Allergy 2009; 2009 Feb 17. [Epub ahead of print]